Lopez-Cruz appeals from his conviction on two counts of transporting aliens in violation of 8 U.S.C. § 1324 (a).

Section 1324(a)(2) is violated if a person transports an alien illegally in this country “knowing that he is in the United States in violation of law, and knowing or having reasonable grounds to believe that his last entry into the United States occurred less than three years prior thereto.”

The sole contested factual issue was the knowledge element. Lopez-Cruz testified that he picked up the two Mexican nationals as hitchhikers and that he did not know they were here illegally. One of the aliens corroborated his story.

The Government’s main ammunition was that, over two years earlier, Lopez-Cruz had transported illegal aliens under almost identical circumstances, although he was not tried for the offense. To prove its theory, the Government evidence was limited to the testimony of a border patrol agent. The agent was permitted to testify, over hearsay objection, about the circumstances of his stopping Lopez-Cruz on the earlier occasion. The agent also testified that the passengers in Lopez-Cruz’ ear told him that they were from Mexico and had no papers to be in the United States.

Even if we assume, arguendo, that the declarations of the aliens were against their interest, the admission of the evidence was error. It is fundamental that the interest exception to the hearsay rule requires the proponent to establish the unavailability of the declarant. (Wigmore, Evidence (3d ed. 1940) §§ 1455, 1456.) The Government did not meet the requirement.

The knowledge issue in this case was pivotal. The jury might have credited the defense testimony on knowledge had it not heard the highly damaging hearsay. Admission of the hearsay under the circumstances was prejudicial error.

Reversed.

. But cf. Scolari v. United States (9th Cir. 1969 ) 406 F.2d 563 , relating to admissions against penal interest. . Both the exception for statements against interest and the requirement of a showing of unavailability of the declar-ant are maintained in the proposed Rules of Evidence for the United States Courts and Magistrates (Rule 804(b) (4), revised draft, March 1971, at 124, 125).