dissenting:

I respectfully dissent from Part III.B of the majority opinion and from the judgment. Part III.B rejects Cruz-Escoto’s contention that the jury instructions inadequately covered his theory of the defense. The majority misconstrues our cases and, consequently, interprets the doctrine of “official restraint” far too narrowly. Although the majority acknowledges in Part III.A that “the geography of the Channel might prevent someone crossing the border from exercising his own free will inside the United States until he passes the permanent post,” Maj. Op. at 1086, inexplicably, it ignores this possibility in its discussion of Cruz-Escoto’s requested jury instructions. The jury instructions requested by Cruz-Escoto would have allowed the jury to consider his theory that the “geography of the Channel,” including the permanent Border Patrol post, placed him under official restraint, even if he was not seen crossing the border. But the jury instructions actually given foreclosed consideration of Cruz-Escoto’s theory of the case.

“It is settled law that a defendant is entitled to have the judge instruct the jury on his theory of the case, provided that it is supported by law and has some foundation in the evidence. A failure to instruct a jury upon a legally and factually cognizable defense is not subject to harmless error analysis.” United States v. Sarno, 73 F.3d 1470, 1485 (9th Cir.1995) (citations, internal quotation marks, and brackets omitted).

Cruz-Escoto requested a jury instruction stating that, “[Wjhen an alien attempts to enter the United States, the mere fact that he may have eluded the gaze of law enforcement, or eluded arrest, for a brief period of time after having come upon United States territory is insufficient, in and of itself, to establish ‘freedom from official restraint.’ ” The district court rejected this proposed instruction and gave the following instruction in its place: “If an alien is under constant surveillance by immigration officers when he entered the United States and the entire time he is inside the United States, he may not be free from official restraint. On the other hand, if an immigration official did not see the Defendant cross into the United States, then the Defendant would not be under official restraint.”

The court’s instruction precluded the jury from considering Cruz-Escoto’s theory of the defense, if the jurors credited the agent’s testimony that he did not see Cruz-Escoto cross the international border. Cruz-Escoto had argued that because of the configuration of the Channel and the fact that a Border Patrol agent is permanently stationed there to monitor the Channel, “unless the person [attempting entry] succeeds in getting past this [Border Patrol] post, that person has not successfully and freely entered the United States.... The mere fact that the border patrol agent at his post did not see the actual crossing of the line or the fence is not dispositive in this case.... ”

Contrary to the majority, I conclude that Cruz-Escoto’s theory of the defense accurately represents the law regarding freedom from official restraint. Even if the Border Patrol agent did not see Cruz-Escoto cross the border, the configuration of the Channel and the permanent Border Patrol post at that location placed Cruz-Escoto under official restraint from the moment he crossed into the United States until he was apprehended. Therefore, Cruz-Escoto was entitled to have the jury consider his theory.

*1092 I disagree with the majority’s assertion that, under our jurisprudence, official restraint requires that a government official actually witness the alien crossing the international boundary line, if the crossing occurs away from an official port of entry. The majority derives this rule from the fact that in other Ninth Circuit cases dealing with official restraint of aliens “sneaking across” the border, the aliens were observed in the act of crossing. See Maj. Op. at 1085-86 (citing United States v. Bello-Bahena, 411 F.Sd 1083 (9th Cir. 2005), and United States v. Castellanos-Garcia, 270 F.3d 773 (9th Cir.2001)).

But the concept of official restraint that underlies our official restraint case law is not so limited. The idea that an alien has not successfully entered the country until he is free from official restraint is rooted in the notion that an alien who is in constructive government custody at all times has not really “made it in” to the United States.

We first adopted the notion that entry requires “physical presence ... accompanied by freedom from official restraint” in United States v. Oscar, 496 F.2d 492, 493 (9th Cir.1974) (citing United States v. Vasilatos, 209 F.2d 195 (3d Cir.1954); In re Dubbiosi, 191 F.Supp. 65 (E.D.Va.1961)). In Oscar , two aliens who attempted to enter by lying to inspectors at a port of entry, claiming that they were U.S. citizens, had not committed the crime of illegal entry because they were “never free from the official restraint of the customs officials at the San Ysidro Port of Entry.” 496 F.2d at 493 . In United States v. Aguilar, 883 F.2d 662 , 681-82 (9th Cir.1989), we affirmed that “surveillance prior to an arrest is official restraint because the alien ‘lacks the freedom to go at large and mix with the population.’ ” (quoting Matter of Pierre, B.I.A. Interim Dec. No. 2239 (Oct. 5, 1973) (later reported at 14 I. & N. Dec. 467 (B.I.A.1973))). As we noted in Aguilar, the concept of “official restraint” is premised on “the theory that the alien is in the government’s constructive custody at the time of physical entry.” 883 F.2d at 683. In Aguilar, we held that the alien was not under continuous official restraint because daily visits to her home by an undercover government agent over a period of months did not amount to constructive custody over that entire period. Id.

Thus, the touchstone of official restraint is whether the alien was actually “free to go at large and mix with the population.” Id. at 682. Because the concept is rooted in the notion of constructive custody, the appropriate inquiry is whether the government retains effective control over the alien. Of. Black’s Law Dictionary 412, 1183 (8th ed.2004) (defining custody as “care and control of a thing or person for inspection, preservation, or security” and physical custody as “[cjustody of a person (such as an arrestee) whose freedom is directly controlled and limited”). While it is true that our cases find that even momentary freedom from government control suffices to establish freedom from official restraint, the controlling question remains whether “an alien is able to exercise his free will subsequent to physical entry.” Aguilar, 883 F.2d at 683 (citing United States v. Martin-Plascencia, 532 F.2d 1316 (9th Cir.1976)).

In cases where the alien crosses the border away from a port of entry, constructive government custody is usually effected through government surveillance. That is the reason that other Ninth Circuit cases dealing with surreptitious border crossings have involved aliens who are seen, either directly or by video or other remote device, as they cross the border. But there is no rule that the only means of achieving official restraint over, or constructive custody of, an alien crossing the *1093 border is through actual observation by government officials. 1

At the area of the Channel where Cruz-Escoto was apprehended, the physical topography along with the degree of government control exerted over the area created a constructive custody situation — without any necessity that the agent have actually watched Cruz-Escoto step over the painted boundary line. 2 The Channel is equivalent to a brightly lit, high-walled corridor crossing the border, with a permanent Border Patrol post at one end. It is fenced along both sides once it enters the United States. Along the south bank, 3 there is double fencing, with an inner fence 15 feet in height and an outer fence of eight feet; a high fence also runs along the north bank. Stadium-style lighting illuminates the Channel at night. An agent sits in a marked vehicle on the north bank of the Channel monitoring the Channel 24 hours a day, seven days a week. Thus, if Cruz-Escoto did cross the border by moving north within the fenced interior of the Channel, he was at all times within this highly-controlled, continuously-monitored space. A jury could justifiably find that he was under effective government restraint while in the United States by virtue of the high fencing around him and the constant monitoring of the corridor by Border Patrol. 4

The unique physical configuration of the Channel distinguishes this case from cases such as Bello-Bahena and Castellanos-Garda, where we held that aliens discovered only a short distance from the border could be deemed to have entered “free from official restraint.” There was no indication in those cases that the aliens’ freedom of movement had been curtailed in any way. Bello-Bahena was found “hiding in some brush” a mile from the border, 411 F.3d at 1086; Castellanos-Garcia was discovered “walking north at least 100 yards from the border” after having scaled the border fence, 270 F.3d at 774 . The majority cites these cases for the proposition that “those who evade government observation while crossing the border are deemed to be free from official restraint, regardless of the distance they travel between entry and arrest.” Maj. Op. at 1085-86 (emphasis in the original). Again, the majority has mistakenly fixated on the criterion of government observation at the precise moment of crossing. The aliens in those cases were not in a contained area, and there was no indication that any form of government control had *1094 been exerted over them from the time they crossed the border until they were apprehended. Since they were found some distance from the border, this was sufficient to show that each had sufficient opportunity to “exercise his free will” free of government control while within the United States. However, Bello-Bahena and Castellanos-García do not establish a general rule that actual government observation is the only means of establishing official restraint over an alien who crosses the border surreptitiously. What remains the controlling rule is whether the “alien is able to exercise his free will subsequent to physical entry.” Aguilar, 883 F.2d at 683.

This case also differs from cases where aliens, in the course of attempting to evade official detection, found themselves in natural environments from which escape was difficult, such as a gorge or very thick brush. See United States v. Vela-Robles, 397 F.3d 786, 789 (9th Cir.2005) (detection by seismic sensor as alien entered natural gorge did not amount to observation or surveillance for purpose of showing official restraint and alien was thus not in the “constant visual or physical grasp of governmental authorities” after crossing border); United States v. Hernandez-Herrera, 273 F.3d 1213, 1216, 1219 (9th Cir. 2001) (alien who was seen crossing the border, but then fled into thick brush “from which there was no escape,” was no longer under official restraint once he left agents’ sight). The government control exercised over a natural gorge or an area of thick brush, even if agents are stationed immediately outside waiting to catch anyone who emerges, does not nearly approach the tunnel-like configuration of the Channel, where a government agent continuously monitors a fenced-in, well-lit space.

Thus, our case law supports Cruz-Esco-to’s theory of the defense. Further, the evidence in this case supported his theory. 5 The physical configuration of the Channel and the location of the Border Patrol permanent post are undisputed. The agent testified that he did not see Cruz-Escoto until he was 100-150 yards up the Channel, meaning that Cruz-Escoto could have crossed the border either by traveling north within the fenced interior of the Channel or by scaling the border fence at some other point and later emerging into the Channel. If the former occurred, for the reasons outlined above, Cruz-Escoto would have been under official restraint the entire time that he was in the United States. Because the evidence left both possibilities open, there was a foundation in the evidence for Cruz-Escoto’s theory and he was thus entitled to an instruction that adequately covered the theory. 6 Sarno, 73 F.3d at 1485 . As the majority *1095 acknowledges, “the geography involved in this case presents a unique situation.” Maj. Op. at 1086. And while I agree that “the jury heard sufficient evidence to decide that Cruz-Escoto was free from official restraint,” id. at 1086, that was not the only possible interpretation of the evidence. Unfortunately, however, the district court gave an instruction which precluded the jury from even considering Cruz-Escoto’s theory, even if the jury accepted the agent’s testimony.

Because Cruz-Escoto was deprived of the opportunity to present his theory of the defense to the jury, I would reverse the judgment of conviction and remand for a new trial. I respectfully dissent.

. The port of entry cases, while not controlling, also illustrate that the key to official restraint is the criterion of government control over the alien, not continuous government observation. Where an alien enters the country at an official port of entry, whether at an airport or a land border, the alien who follows government-designated procedures is not deemed free from official restraint until she exits the customs inspection area, because until then she is not "free to exit thefport of entry] and ‘go at large and mix with the general population.’ ” Sidhu v. Ashcroft, 368 F.3d 1160, 1165 (9th Cir.2004) (quoting Correa v. Thornburgh, 901 F.2d 1166, 1172 (2d Cir. 1990)); see also United States v. Zavala-Mendez, 411 F.3d 1116, 1120-21 (9th Cir.2005) (relying on the idea that an alien who presents herself at a border station is not "found in” the United States within the meaning of 8 U.S.C. § 1326 (a)).

. There is no border fence crossing the Channel but the international boundary is marked by a yellow painted line across the cement bottom of the Channel. When the Channel is dry, as it was at the time of Cruz-Escoto’s crossing, the line is readily visible across the width of the Channel.

. Immediately after the Channel enters the United States, it turns and runs west toward the Pacific.

. Thus, the Channel is the virtual equivalent of a tunnel under the border with a Border Patrol agent stationed at the end of the tunnel as it emerges on the U.S. side of the border.

. While recognizing that Cruz-Escoto’s requested instruction was a correct statement of the law, the majority states that there was no foundation for it here because "[t]here was never a question of whether the government surveillance amounted to constructive official restraint resulting from brief periods of interruption.” Cruz-Escoto’s theory, however, relied on the idea that the presence of a government agent observing the Channel, together with the topography of the Channel itself, placed him in constructive custody — even if the agent did not actually observe Cruz-Esco-to until he was already within the United States. Therefore, it was important to his defense that the jury be instructed that, in the circumstances of the topography of the Channel, brief periods of interruption in the government surveillance while Cruz-Escoto was still in the Channel, did not preclude a finding of official restraint.

. I agree with the majority that a rational fact-finder could have found that Cruz-Escoto entered free from official restraint, because it is unclear whether Cruz-Escoto entered the United States by moving up the lighted interi- or of the Channel or by scaling the international boundary fence at some other point and only later scaling the inner Ballard fence to enter the Channel interior. The agent's testimony that Cruz-Escoto was running northwest, as if he had come from the southeast, strongly suggests that Cruz-Escoto came *1095 across the border within the Channel. The agent also testified, however, that it is common for aliens to scale the border fence at other points along the Channel, where there are more shadows. It is for this reason that I agree with the majority’s rejection of Cruz-Escoto's claim that his motion for acquittal should have been granted.