DALLAS (CBSDFW.COM/AP) – A 28-year-old Dallas-area man has been sentenced to about six months in jail after pleading guilty to a charge in an ongoing voter fraud investigation.

A statement Wednesday from the Dallas County District Attorney’s Office says Miguel Hernandez pleaded guilty to a single count of using an unlawful method of returning a marked ballot.

He was accused of visiting a woman in April and collecting her blank absentee ballot, then filling it out and forging her signature before mailing it to the county. Dozens of senior citizens in West Dallas and Grand Prairie filed complaints about receiving mail-in ballots they had not requested.

The investigation began after hundreds of mail-in ballots were sequestered from the Dallas city elections in May. The case caused 700 suspicious mail-in ballots to be sequestered.

“This is the first of many milestones in the ongoing investigation into voter fraud in Dallas County,” DA Johnson said. “As I have stated many times before, the right to vote is the cornerstone of our democracy. We must protect the process so that all citizens may have confidence in the system. It is my hope, with this conviction, that we will send a message to anyone who dares to threaten the integrity of the voting process. We will not tolerate it and you will be brought to justice.”

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)