No direct evidence points to McCotter's involvement and he isn't charged, Michigan Attorney General Bill Schuette said at a morning news conference. But Schuette said his fellow Republican provided "no supervision whatsoever" to the employees.
Schuette said "people were dummying up, phonying up petitions" in part by lifting signatures that were gathered in 2006 on petitions for this year's election.
"They copied petitions, submitted petitions falsely signed by circulators and did cut-and-paste jobs that would make an elementary art teacher cringe," Schuette said. "The buck stops at the top, but in this case Thad was asleep at the switch."
Schuette spokeswoman Joy Yearout said McCotter was not legally required attest to the accuracy of the nominating petitions before they were submitted.
McCotter did not immediately respond to phone messages seeking comment after Schuette's news conference, but he released an emailed statement thanking the attorney general and his office "for their earnest, thorough work on this investigation, which I requested, and their subsequent report."
He added that for him and his family, "this closure commences our embrace of the enduring blessings of private life."
McCotter's former deputy district director Don Yowchuang, district director Paul Seewald, district representative Mary Melissa Turnbull and staffer Lorianne O'Brady face charges ranging from forgery and conspiracy to falsely signing election documents.
Yearout said Yowchuang and Seewald were scheduled to be arraigned Friday. She did not have information about court appearances for Turnbull or O'Brady.
No phone listing could be found Thursday for Yowchuang, who faces 17 charges, or O'Brady, who is charged with five counts of falsely signing a nominating petition as circulator.
A phone call to the home of Seewald, who faces 10 charges, went answered. A listing for Turnbull, who faces two charges, was disconnected.
McCotter's resignation last month capped a bizarre political downfall for the guitar-slinging Republican who ran a little-noticed campaign for president in 2011.
The 46-year-old McCotter's failure to submit the needed signatures paved the way for tea party-backed Kerry Bentivolio to win the GOP nomination in Tuesday's primary. Bentivolio faces Democratic Dr. Syed Taj in the Nov. 6 election.
McCotter's staff turned in 2,000 signatures supporting his candidacy, twice as many as needed to be eligible for the Aug. 7 primary ballot. But 80 percent were found to be fake or duplicated. McCotter initially said he would conduct a write-in campaign but eventually dropped the effort.
The attorney was first elected to the House in 2003 after serving as a state senator and county commissioner. A member of the House Financial Services Committee, McCotter also was a loud critic of big government.
He was known among his colleagues and constituents for his flowery rhetoric and humor, and took pride in his talents as a guitarist. He played with a congressional rock band called "The Second Amendments," and after announcing his long-shot bid for the presidency last year, he jammed to a Chuck Berry tune on a guitar designed to look like an American flag. He finished last in the Iowa straw poll.