An internal investigation into a national jackpot-fixing scandal has concluded that a single former lottery employee was responsible for any drawings that were manipulated, but it failed to uncover proof of his guilt.

The report for the Multi-State Lottery Association found that its former security director, Eddie Tipton, had no help from other employees. But investigators said they found no smoking gun proving criminal activity, such as the manipulation of computers that pick numbers.

The April 29 report was obtained by The Associated Press.

Tipton was convicted last year of tampering with a drawing for a $16.5 million jackpot after he was seen on video buying the winning numbers at a Des Moines gas station. He's awaiting trial on allegations that he conspired with associates to collect jackpots in several states.