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

Mail Vicki Lyn Stuart and Sally Jane Maxedon were arrested on suspicion of identity theft, attempting to influence a public official and forgery, according to their arrest affidavits. There were no attorneys listed to represent them in court filings yet. Neither has yet been formally charged.

In a statement, 21 District Attorney Dan Rubinstein’s office said its investigators began an investigation on Oct. 21 after residents who had never mailed in a ballot or received a mail-in ballot were notified that the ballots their ballots were not counted due to 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 hassles on Election Day. Ballots are mailed to voters, who can either return them by mail or leave them in the ballot box. Election workers check signatures on envelopes containing mail-in ballots against voter signatures on file to ensure they are submitted by the voter to whom the ballot was mailed.

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

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

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

Mesa County is home to former County Clerk Tina Peters recently convicted to prison for a data breach scheme stemming from false claims about automated voter fraud in the 2020 presidential race.