Report: 'Kristen' is Ashley Youmans — now known as Ashley Alexandra Dupre.

WASHINGTON (CNN) — Federal agents have determined New York Gov. Eliot Spitzer used a high-priced call-girl ring at least eight times in recent months, and agents had him under surveillance twice this year, sources familiar with the investigation said Wednesday.

Spitzer announced his resignation Wednesday, two days after reports of his connection to the Emperors Club VIP became public.

He has not been charged with a crime.

He told reporters Wednesday, "I cannot allow my private failings to disrupt the people's work."

The resignation will take effect Monday. Watch Spitzer resign »

The sources said the investigation began when New York's North Fork Bank notified the Treasury Department about suspicious transfers of money from Spitzer's bank accounts. That investigation led agents to the alleged organizers of the prostitution ring, four of whom were charged in a criminal complaint last week, the sources said.

A grand jury in New York is likely to hear evidence in the case soon, said Kathleen Mullin, an attorney who said she represents one of the ring's employees. Mullin would not identify her client, but said she was not the woman identified only as "Kristen" linked to Spitzer in court papers.

She said her client and other women who worked for the Emperors Club have been asked to testify before the grand jury.

Asked if her client had any encounters with Spitzer, Mullin said, "We have no information regarding the governor."

Wiretaps on suspected members of the ring, authorized in January, yielded more than 5,000 telephone calls and text messages and another 6,000-plus e-mails, according to court papers. In those intercepts, the organizers told clients how to arrange and pay for their trysts, a federal agent's affidavit states.

The affidavit identified clients by number, with Spitzer designated "Client 9," a source with knowledge of the investigation told CNN this week. Sources familiar with the investigation said federal authorities Wednesday were trying to clamp down on leaks of the investigation's details. See a timeline of the investigation »

The affidavit states "Client 9″ paid $4,300 for 2½ hours with a call girl he arranged to meet at Washington's Mayflower Hotel, with some of that a deposit on a future session. Court papers state he also paid for train tickets, cab fare, mini-bar and room service charges for Kristen — a 5-foot-5, 105-pound brunette he arranged to meet the night of February 13.

Kristen is a 22-year-old would-be singer from New Jersey, The New York Times reported Wednesday.

The newspaper said Ashley Youmans — now known as Ashley Alexandra Dupre — was identified in court documents as Kristen.

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Watch Koch's interview on The Situation Room.

(CNN) - As the political world comes to grips with revelations of New York Gov. Eliot Spitzer's involvement in a high-priced prostitution ring, former New York City Mayor Ed Koch told CNN's Wolf Blitzer that he thought Spitzer's behavior was "irrational."

"I think there's a screw loose," says Koch. "I believe that his behavior, beginning with his becoming governor, has been irrational. And, what he did is to indicate that he doesn't play by the regular rules, that regular rules don't apply," Koch adds.

Koch also shares his thoughts on Spitzer's political future and whether he thinks Spitzer was targeted by political enemies in New York.

–CNN Associate Producer Martina Stewart

CNN=Politics Daily is The Best Political Podcast from the Best Political Team.

(CNN)— The political world — inside and outside New York, Republican and Democratic — was rocked Monday by reports of New York Gov. Eliot Spitzer's involvement in a prostitution ring.

In the latest episode of CNN=Politics Daily, Mary Snow reports on the Spitzer scandal and Kelli Arena reports on the ongoing criminal investigation into the prostitution ring that has ensnared Spitzer and his political career.

Senior Political Correspondent Candy Crowley is on the campaign trail in Jackson, Mississippi and reports on how Sen. Barack Obama has responded to the Clinton campaign's repeated suggestions that he would make a suitable vice presidential running mate to Sen. Clinton.

Suzanne Malveaux is also out on the trail in Pennsylvania — the next big delegate prize in the Democratic race.  But, before Pennsylvania's primaries, the Democratic Party is looking back to past primaries in Florida and Michigan.  Malveaux explains what the party may do to allow delegates from both states to participate in the convention and play a role in deciding whether Clinton or Obama will face off against Sen. John McCain.

Finally, Dana Bash reports on McCain's comments Monday about his health.

Click here to subscribe to CNN=Politics Daily.

–CNN Associate Producer Martina Stewart

New York Gov. Eliot Spitzer has admitted involvement in a prostitution ring, The New York Times reports.

(CNN) – Gov. Eliot Spitzer said he "acted in way that violates his obligation to his family," speaking hours after the New York Times reported he told senior administration officials he had been involved in a prostitution ring.

"I apologize first and most importantly to my family. I apologize to the public, to whom I promised better," he said.

He did not elaborate on the paper's claims and did not take any questions after making his statement.

"I am disappointed that I failed to live up to the standard I expected of myself," he said

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WASHINGTON (CNN) –Deputy Attorney General Mark Filip, who was sworn in this morning, stopped by the Justice Department press room to pay a courtesy visit to journalists who work at Main Justice.

Shortly after Filip sat down to chat informally with about a half dozen wires service reporters and network news producers, the CNN monitors began to carry the statement by Elliot Spitzer apologizing for his behavior.

I abruptly jumped up, boosted the volume, and asked the brand new second-highest ranking law enforcement official in the nation if he could kindly hold on a minute, as everyone’s attention turned to Spitzer’s words. “No problem. I want to see it too,” Filip said. He made no other comment on the matter, which presumably involves federal prosecutors and investigators who had been officially under his control for about five hours.

Filip said he hopes in his ten months as Deputy to Attorney General Michael Mukasey to be active in areas that are largely non-partisan. Filip acknowledged the election year could limit what can be accomplished, but he singled out the theft of Intellectual Property as an area of criminal law where he hopes he can make a difference before the Administration term concludes.

Filip gave up a lifetime appointment as a federal judge in his native Chicago to accept the number two post at the Justice Department. Filip began his career as an Assistant U.S. Attorney in Chicago.

–CNN's Terry Frieden

New York Gov. Elliot Spitzer explains why he dropped his license plan for illegal immigrants.

WASHINGTON (CNN) — New York Gov. Eliot Spitzer said Wednesday he is giving up his proposal to grant driver's licenses to undocumented workers, a plan he said would "improve the safety and security of the people of my state."

Spitzer said he was giving up because he had concluded that "New York state cannot successfully address this problem on its own."

He said he wanted to act because of the failure of the federal government to deal with immigration policy and the impact that failure was having on New York.

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