HARRISBURG, Pa. – A criminal investigation is underway in the crucial presidential battleground of Pennsylvania after election workers in one county flagged about 2,500 voter registration forms for potential fraud. Two other counties were alerted to look for similar problems.

The forms arrived at the Lancaster County elections office shortly before the state’s registration deadline last month and appear to have been part of a larger effort to register people, officials said Friday. Some had fake names, suspicious handwriting, questionable signatures, incorrect addresses or other problematic details.

Two other counties “received similar requests” and were notified to look into them, Lancaster County District Attorney Heather Adams said at a news conference. She declined to name the other counties.

“It appears to be an organized effort at this point,” said Adams, a Republican. “But of course it’s an ongoing investigation. And we’ll look at who exactly participated in it and how far it goes.”

The set of claims was separated during the investigation, preventing ballots from being sent or cast to individuals until they are deemed valid. Pennsylvania’s 19 electoral votes are in contention as polls show the state’s presidential race is a close race.

“The truth is, we have withheld it,” Lancaster Commissioner Ray D’Agostino, a Republican who chairs the board of elections, said at the news conference. “It’s not fair. It’s illegal. It is immoral. And we found him and we’re going to deal with him.”

Adams and members of the county board of elections did not say who dropped off the forms or who they worked with.

D’Agostino said the petitions were not limited to one party and were collected in various places in Republican-majority Lancaster.

The Pennsylvania Department of State issued a statement Friday praising election workers “for their diligent work in identifying this potential fraud and bringing it to the attention of law enforcement.” The state attorney general’s office, which was also contacted by Lancaster officials, declined to comment.

About 3 out of 5 of the apps that have been fully investigated so far have had problems, Adams said. Other applications among the 2,500 have been verified as accurate and are being processed as normal, she said.

Most of the claims were dated Aug. 15, and most were from Lancaster City. Adams said the applications were collected as part of a “large scale canvassing operation”.

“In some cases, the applications contained correct personally identifiable information, such as the correct address, correct phone number, date of birth, driver’s license number and social security number – but the people listed on the applications informed detectives that they did not they requested the form. Adams said. “They did not complete the form and verified that the signature on the form was not theirs.”