Regarding the consent issue, the government's burden is to prove that "consent was, in fact, freely and voluntarily given." The government stated that Knoll was warned in advance that he would be searched at the ticket booth, it was alleged that and he still had time to refuse. Both the District Court and the United States Court of Appeals for the Eighth Circuit found that this did not constitute consent a meaningful sense, as forcing the defendant to choose between exercising his Fourth Amendment rights to refuse to be searched and his right to travel constituted coercion.

Regarding the extraordinary nature of the circumstances, there was no evidence that Knoll showed any reason to give the suspicion he might carrying explosives or weapons, although the court did state that the inspection of the attache case was justified by the dangers posed by hijacking. But inspecting what was inside the envelope exceeded the scope of the permissible search under the circumstances, given there was no reason to suspect that there was explosives in the envelope, given the size of the package.

The District Court had granted the defendant's pretrial motion to suppress the amphetamine, holding that while it was reasonable to inspect the defendant's attache case, it was not reasonable to inspect the contents of the small...

The court called the U.S. Marshal's testimony that nitroglycerin or other explosives could have been placed in the envelope subjective and based on limited military experience, and it did not seem reasonable to examine the envelope's contents given the circumstances. Furthermore, the Marshall's objective behavior indicated that at that point, having found the envelope, he was more interested in finding contraband. If he had seriously believed that weapons that could have been used to hijack the plane or dangerous explosives were in the envelope, the Marshall would have taken precautions like clearing the area of people or removed the suspect case and envelope to another area, away from all individuals present at the scene.
Conclusion

The District Court's decision was affirmed -- there was no reason to assume consent, and the search of the envelope was not valid because although the original search may have been valid for security purposes for explosives, the search of the envelope and the method seemed designed for contraband, which was not the reason the search under extraordinary circumstances had taken place.

Works Cited

United States v. Kroll. United States Court of Appeals for the Eighth Circuit. 481 F.2d 884

July 10, 1973. http://www.altlaw.org/v1/cases/462836