(CNN) -- A Michigan man and woman convicted of trying to extort $680,000 from "Glee" actor John Stamos by threatening to sell compromising photos were each sentenced to four years in prison Friday. 

U.S. District Judge R. Allan Edgar in Marquette said the photos never existed, according to a federal prosecutor. 

Scott Edward Sippola, 31, and Allison Lenore Coss, 24, could have faced up to nine years in prison for convictions of conspiracy and interstate communications to extort money. 

Assistant U.S. Attorney Paul Lochner said a statement from Stamos was read in court. In it, Stamos said he had been slandered and his reputation impugned. Lochner said the judge ascertained that the conspiracy wasn't just a "foolish lark." 

In a presentence filing, Sippola admitted his conduct "was awful." 

"I sought to exploit my knowledge of the personal weaknesses of a perfect stranger for my own undeserved financial gain," Sippola wrote. 

"The case was made by the fact that these defendants made threats to damage his [Stamos'] reputation in order to have him pay them," Assistant U.S. Attorney Maarten Vermaat said after the July verdict in Marquette, Michigan. 

According to CNN affiliate WLUC, prosecutors said that Coss and Sippola told Stamos that if he didn't give them the money, they would sell embarrassing pictures of him allegedly using drugs to tabloid publications. 

Vermaat said the defendants sent about 40 e-mails to Stamos threatening to sell the photos. FBI agents got involved and started monitoring Stamos' e-mail account and "eventually communicated by cellular telephone with the defendants pretending to be Mr. Stamos' business manager." Sippola and Coss were arrested in December 2009 at an airport, a pre-arranged dropoff spot for the money. 
What agency investigated the crime?
FBI 