NEW YORK -- WNBC.com's Jonathan Dienst has reported exclusively that the ongoing criminal investigation into former Westchester District Attorney Jeanine Pirro has broadened. Investigators are looking into whether Pirro improperly used the resources of the district attorney's office for her political campaign work.

Sources say investigators are very interested in records and computer files from around the time Pirro was planning her Senate run against Sen. Hillary Clinton.

Dienst has learned that, for months, federal prosecutors, FBI agents and local investigators have been pouring over documents from the Westchester District Attorney's Office, many of those records dating to 2004 and 2005. That was around the time Pirro was launching her soon-to-be abandoned bid for Clinton's seat.

Sources familiar with the investigation say federal and state prosecutors want to know if Pirro improperly put resources available to her as Westchester District Attorney toward campaign work. One key question: whether Pirro or her staffers conducted background checks on campaign donors using computers and databases inside the District Attorney's office.

Pirro dropped out of the Senate race, and went on to become the Republican candidate for New York State Attorney General, losing to Democrat Andrew Cuomo.

Dienst has learned that federal agents have also been questioning former members of Pirro's campaign staff in recent weeks.

Pirro's lawyer, Charles Stillman, said that background checks were done on campaign contributors, but they were legal.

"In order to preserve the integrity of investigations by the Westchester District Attorney's office, background checks were done to be sure that no contributor was the subject or target of any pending investigation. Ms. Pirro and we believe that her conduct was perfectly appropriate."

A spokesman for the United States Attorney's Office said he would not comment on an ongoing investigation. The FBI, IRS, the Westchester County district attorney and the city Department of Investigation all had representatives decline comment as well.

This is the second time in four months that Dienst has uncovered an investigation into Pirro.

In September, Dienst first reported that Pirro, then a candidate for New York attorney general, was under federal criminal investigation. At that time, as many as six different federal and local agencies were reviewing wiretapped conversations between Pirro and former New York City police Commissioner Bernard Kerik.

Her calls to Kerik centered on her alleged attempts to try to secretly record her husband Albert Pirro having an alleged affair on his boat. Investigators are still looking into whether those recordings between Pirro and Kerik amount to a conspiracy to commit illegal eavesdropping. It's an allegation Pirro has denied repeatedly.

The questions about whether she improperly used her office to help her political campaign come as reports surfaced those investigators were also looking into tax questions regarding Pirro's efforts to start a side jewelry business.