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Justice Department investigating embattled Rep. Aaron Schock

Rep. Aaron Schock announced this week that he is resigning from Congress. (AP Photo/Seth Perlman, File)

The Department of Justice is investigating whether embattled Rep. Aaron Schock (R-Ill.) broke any laws, two people familiar with the case confirmed Friday, a sign the Republican may face lingering legal issues even as he prepares to step down from Congress.

It was not immediately clear how far along the investigation is or what charges investigators may be contemplating, but Schock's spending from his taxpayer and campaign accounts and some of his mileage reimbursement claims have come under intense scrutiny following weeks of media reports that raised questions about his spending habits.

Word of the Justice Department probe, which was first reported Friday by CNN, came three days after Schock, 33, abruptly announced that he would resign his House seat as of March 31.

Rep. Aaron Schock (R-Ill.) resigned from Congress amid allegations he misused funds. The Washington Post's Ben Terris explains a few things lawmakers might want to avoid if they want to keep their seats. (Video: Julie Percha/The Washington Post)

Schock's office did not immediately respond Friday to a questions about the Justice Department investigation.

The people describing the case requested anonymity because they were not authorized to discuss the matter on the record. The government plans the has convened a grand jury to look at evidence related to Schock, they said.

[Related: Who had the worst week in Washington? Rep. Aaron Schock.]

Schock's former communications director Ben Cole, who resigned earlier this year after racially-charged online comments he made were reported by the media, is among those who have been subpoenaed, according to a person with knowledge of the matter.

Schock announced Tuesday that he would step down from his seat. His decision caught his colleagues by surprise, even as it came on the heels of weeks of reports about private plane travel, overseas trips and ticket purchases. The Washington Post reported in February that Schock had remodeled his office after the popular TV show "Downton Abbey," attracting attention to his expenditures.

One of the people familiar with the case said the investigation of Schock has been going on for a matter of weeks. The other, a U.S. official, said some law enforcement officials were taken by surprise when he announced his resignation.

Schock will officially step down on March 31. His resignation could spare him from facing a probe from congressional ethics investigators, even as he remains under scrutiny by legal authorities.

Schock is in his fourth term in Congress. His seat is expected to remain in Republican hands in a special election later this year.

Read more on Aaron Schock:

Aaron Schock: The congressman felled by Downton Abbey

Rep. Aaron Schock announces resignation in wake of spending probe

He’s got a ‘Downton Abbey’-inspired office, but Rep. Aaron Schock won’t talk about it.

Schock faces preliminary review of spending practices