In a perjury case, it's the word of the accuser against the word of the defendant, plus "evidence." No corroborating witness is needed. The "evidence" could be circumstantial, or even another accusation--such as (as Olivant noted) Cicci's testimony that Michael was the head of the family. Cicci didn't have to have heard Michael give any orders--the fact that he was in the family and said Michael was the head, when combined with Frankie's testimony, could have been enough to bring Michal to trial on perjury charges.

It was a beautiful trap. The government didn't have to prove that Michael had committed any of the crimes Questadt and the Senators accused him of--all they needed to do was to use Frankie's testimony and "other evidence" to recommend to a US Attorney that Michael be indicted for lying under oath. In our adversarial system of justice, once a case goes to trial, the issue isn't innocence or guilt, or even right or wrong: it's who wins and who loses. Even a weak case can result in a conviction. In Michael's case: even if he were acquitted of perjury, or if he were convicted but had his conviction overturned on appeal, his reputation would be ruined. Simply being indicted for a serious crime like perjury would be enough for the Nevada Gaming Commission to put his name in the "Black Book" and to start proceedings to yank his casino licenses.

(N.B.: In one of the most celebrated perjury cases in the last century, Alger Hiss, a highly regarded State Department official, was accused by Whittaker Chambers, a Time Magazine editor, of having been a Communist and a Soviet agent. Hiss made a powerful defense, and even denied having ever met Chambers. The House Un-American Activities Committee was never able to prove that Hiss was a spy. But, thanks to Richard Nixon, one of the Committee's new members, they proved that he had met Chambers and did know him. Result: Hiss went to prison on a perjury rap. That's a parallel to what might have happened to Michael had Frankie testified.)