Local police in Arlington, Va., have opened a criminal investigation after a secretly recorded video showed the son of a Democratic congressman apparently advising someone who claimed to be looking for ways to commit voter fraud.

In a brief statement, the Arlington County police department and attorney's office said they were "aware" of the video "allegedly depicting" Patrick Moran, son of Virginia Rep. Jim Moran, "assisting another to vote illegally."

"The Arlington County Police Department has initiated a criminal investigation of this matter," the statement said.

Patrick Moran has resigned from his father's campaign in the wake of the video. Moran was secretly recorded by controversial conservative activist James O'Keefe's group, Project Veritas.

After Moran was approached, and at first resisted the questions, he did eventually give tips on how to forge ID's -- like a utility bill -- to illegally cast ballots for 100 people he was told were not going to show up to vote.

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The audio on the tape is unclear at times, but Moran appears to say: "With the new voter ID laws ... he'll need bills. He'll need something with a name and their address on it.

"There'll be a lot of voter protection, so if they just have, you know, just the utility bill or a bank statement -- bank statement would obviously be tough -- but they can fake a utility bill with ease."

Patrick Moran told The Associated Press that he was not taking the person seriously, and thought he was unstable. He was merely humoring him, Moran claimed, but said in hindsight he should have walked away. "At no point have I, or will I, ever endorse any sort of illegal or unethical behavior," he told the AP.

But O'Keefe blasted Moran, and took issue with his claims that he was just playing along. "Moran brainstorms with our reporter on the most effective manner in which to commit voter fraud for the goal of circumventing voter ID laws; he suggests that our reporter should fabricate utility bills and impersonate poll workers over the phone, calling the unsuspecting voters before compromising their vote to ensure they hadn't voted already," O'Keefe wrote in an email to Fox News, calling the tape "manifestly damning."

The flap, though, has caused problems for Rep. Jim Moran's campaign. Patrick Moran resigned as field director Wednesday. Then his opponent, Republican Patrick Murray, put out a statement calling for an investigation by "local, state and federal election officials," adding that "it is not clear whether or not there was any wrongdoing."

"The integrity of our nation is at stake, and it appears that my opponent's campaign seems prepared to undermine free and fair elections right here in Virginia," he said.

The Arlington County Democrats, in Virginia, also said that they have asked Pat Moran "not to return to our offices."

The controversy comes as Moran and two other Virginia Democratic congressmen demand a federal investigation into a case where a 23-year-old worker for a Republican contractor was charged with 13 counts of destroying voter registration forms -- after allegedly dumping them in a mall Dumpster.

The local sheriff said it appears what happened was not widespread, but limited.

Virginia Attorney General Ken Cuccinelli, a Republican, is investigating that case and said he will protect the election's integrity.

"I wouldn't say there's any particular pattern that we've observed around the commonwealth, this is a continual problem. Human nature is what it is and people are going to continue to break the law and cheat and that tends to not know any sorts of boundaries, left, right, up, down. We're going to go after it wherever it exists," he told Fox News. "The attorney general is going to do everything that he can to keep their vote secure and to make sure it's not diluted by illegal voting and also to protect their own ability to get in there and cast their own vote by protecting their registration, which is what's at stake in the case that we've been called into."

If you suspect voter fraud where you live, email voterfraud@foxnews.com

Fox News' Meredith Orban contributed to this report.