Following multiple Denver7 reports about forged signatures in the petition process for the GOP U.S. Senate primary ballot, a liberal group has called on two district attorneys to open a criminal investigation.

ProgressNow Colorado sent a letter to Mitch Morrissey and Peter Weir, the District Attorneys in Denver and Jefferson County, respectively.

"We ask that you pursue a criminal investigation of Jon Keyser and his campaign immediately. Colorado voters must have full confidence in the integrity of the election process," wrote ProgressNow Colorado Executive Director Alan Franklin.

When a candidate for U.S. Senate petitions their way onto the ballot, they are required to collect 1,500 valid signatures from each of the state's seven Congressional Districts, for a total of 10,500 signatures. The voters signing the petition must belong to the same political party as the candidate, in this case they must be registered Republicans. The voter signing the petition must list their address and that address must match the one on file with the Secretary of State's office. If that voter signs multiple petitions, the candidate who turns in their petition first gets credit for that signature.

Denver7 has talked to several people whose names appeared on petitions for Jon Keyser in the first congressional district who claim their signatures were forged. Many of those signatures were collected by a woman named Maureen.

MORE | See if your name is on a GOP U.S. Senate petition

Keyser has already gone to court once to earn a spot on the ballot.

Keyser submitted 16,067 signatures, with 11,436 accepted. However, he fell 86 signatures short in Congressional District Three. The Secretary of State rejected signatures over technical errors made by a signature collector. The home address the collector provided on the petition affidavit was different than the address on file with the Secretary of State. Keyser challenged the ruling in court and a judge, who is allowed more leniency than the Secretary of State, determined the rejected signatures could count.

Marshall Zelinger is a Peabody Award-winning journalist. He covers politics, breaking news and investigations for Denver7 and co-hosts Politics Unplugged on Sunday afternoons on Denver7. Follow him on Twitter and Facebook. Email your story tips to Marshall at Marshall@thedenverchannel.com.

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