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DENVER (AP) — A postal worker and her friend were arrested Wednesday in connection with the forging of stolen mail ballots in an alleged attempt to test the security of Colorado’s voting system, according to court documents.

Mail carrier Vicki Lyn Stuart and Sally Jane Maxedon were arrested on suspicion of identity theft, attempt to influence a public servant and forgery, according to their arrest affidavits. There were no attorneys listed as representing them yet in court records. Neither has been formally charged yet.

In a statement, the office of 21st District Attorney Dan Rubinstein said its investigators began a probe on Oct. 21 after residents who never submitted a ballot or ever received a ballot in the mail were notified that their ballots were not being counted because of discrepancies with their signatures.

Colorado overwhelmingly votes by mail, which officials tout as a safe and convenient method that avoids long lines and last-minute problems on Election Day. Ballots are mailed to voters who can either return them by mail or drop them off in ballot boxes. Election workers check the signatures on the envelopes holding mail ballots against voter signatures they have on file to ensure they are being submitted by the voter the ballot was sent to.

The investigation into the stolen and forged ballots was announced by Colorado Secretary of State Jena Griswold last month.

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At the time, she said at least 12 mailed ballots were stolen in Mesa County and sent in with fraudulent votes, three of which slipped past county election officials and were counted for the election that ended Tuesday. Because ballots themselves are not signed, once they are removed from the signature envelope, there is no way to identify them.

According to the arrest affidavits, victims are still being located and confirmed, and investigators believe there could be over 20 people whose ballots were stolen.

Mesa County is where former county clerk Tina Peters was recently sentenced to prison for a data-breach scheme spawned from false claims about voter machine fraud in the 2020 presidential race.