Bernard Kerik (search), who withdrew his nomination for homeland security secretary after disclosing that he had not paid all required taxes for a nanny, did not fill out a background form when he was appointed police commissioner in 2000, city officials said.

The Department of Investigation said it is examining Kerik's tenure as head of the New York Police Department under former Mayor Rudolph Giuliani (search) but declined to cite specifics.

"DOI is absolutely seeking facts and doing interviews and looking for answers," the department said in a statement Thursday.

Under the current mayoral administration, those nominated as agency commissioners must fill out background forms. A DOI spokeswoman declined to say whether that rule applied to previous administrations.

Kerik, 49, was tapped by President Bush earlier this month to head the Department of Homeland Security (search). He abruptly withdrew his name from consideration after revealing that he had not paid all required taxes for a family nanny-housekeeper and that the woman may have been in the country illegally.

A rash of other revelations soon followed, including allegations that he had connections with people suspected of doing business with the mob and accusations that he had simultaneous extramarital affairs with two women.

According to DOI findings, Kerik submitted a background form when he became commissioner of the Department of Correction in 1998 but did not fill one out when he was appointed police commissioner two years later.

Although he did not fill out the form, the DOI statement said, "we have been told there was communication between City Hall and DOI regarding Mr. Kerik's appointment to police commissioner."

Giuliani had asked the Department of Investigation for a background report on Kerik, Giuliani spokeswoman Sunny Mindel said. She declined further comment.

DOI spokeswoman Emily Gest declined to say whether Giuliani asked for such a report.

Kerik's lawyer, Joseph Tacopina, said his client completed a background report as head of the correction department. He said Kerik also prepared financial disclosure forms in each of the years he served as commissioner of the correction and police departments.

Kerik, who works for Giuliani's consulting firm, Giuliani Partners, has apologized "to anybody who's been brought into this unnecessarily," including Giuliani, a close friend who had promoted his Bush cabinet candidacy.

"What happened between me and the White House is my fault and nobody else's," Kerik told reporters this week.