Officials with the Dallas County District Attorney’s Office has opened an investigation into more than 1,200 suspicious mail-in ballot applications submitted in this year’s primary election.

It is the second year in a row that the electoral system of the second-largest city in Texas has come under scrutiny. Last year, in advance of municipal elections, authorities said they had received some 700 tainted mail-in ballots.

The current case involves 459 questionable votes cast from those 1,200 applications. Dallas County Elections Administrator Toni Pippins-Poole told The Dallas Morning News that her office alerted prosecutors after flagging suspicious ballots, which can be cast by the elderly or disabled, and others who are out of town on Election Day.

Red flags included suspicious dates on the applications that were many months before the election and — in some cases — hundreds of applications arriving at one time in a single FedEx box.

According to Pippins-Poole, four of the voters whose names appeared on applications for ballots are dead — including one who died several years ago.

“We want to let people know that we are serious,” District Attorney Faith Johnson told the paper. “It’s not about a political party. People have the right to have their votes counted.”

Logan Churchwell, a spokesman for the Public Interest Legal Foundation (PILF), told LifeZette that the current cases are unrelated to last year’s case but occurred in many of the same neighborhoods.

“This is a new crop of fraudulent applications, leading to fraudulent votes, potentially,” he said. “The reality is it probably has multiplied, nearly doubled.”

Churchwell, whose organization fights for clean elections and accurate voter rolls, said mail-in balloting in most states is the easiest voting method to cheat and the hardest to prevent fraud.

“That kind of shows, once again, the weaknesses of our system,” he said.

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Catherine Engelbrecht, the founder of the election integrity group True the Vote, agreed mail-in voting is particularly vulnerable.

“I don’t know the particulars of this case,” she said. “However, just broadly speaking, mail-in voting is the soft underbelly of almost every election process, and Dallas is no exception.”

It is vital that election officials do whatever they can to detect and punish fraud, Engelbrecht said.

“That puts everyone at risk,” she said. “Every fraudulent vote cancels out the vote of a legitimate voter.”

Voter fraud allegations came to light last year after senior citizens in Dallas and Grand Prairie, a suburb between Dallas and Fort Worth, complained that they had received mail-in ballots they never requested. Investigators soon linked about 700 applications to a single witness named “Jose Rodriguez.”

Prosecutors brought charges against Miguel Hernandez, 27, whom a West Dallas woman identified as “Jose Rodriguez,” according to The Dallas Morning News.

Related: Unsolicited Absentee Ballots Raise Eyebrows in Dallas

The Texas Legislature responded to the fraud reports by increasing penalties for voting crimes. In addition, new rules in Dallas County require candidates to be officially filed to run for office before campaigns can gather 200 applications for absentee ballots.

Churchwell said the state could take other steps to make mail-in voting more secure. He suggested requiring voters and witnesses to submit a driver’s license number, a passport number or other government-issued, unique number that is not public record on applications.

That, Churchwell said, would make it much harder to apply fraudulently for large numbers of ballots. He said Kansas has a similar law that has proved effective.

“Voter ID has a place here,” he said. “We just need to think about it in a different way.”

PoliZette senior writer Brendan Kirby can be reached at [email protected]. Follow him on Twitter.