Charles Sykes, File, Associated Press
FILE - New York Police Commissioner Raymond Kelly and son Greg attend the New York City Police Foundations 31st Annual Gala in New York, in this March 3, 2009 file photo. Kelly, son of the city police commissioner, is under investigation by prosecutors and denies any wrongdoing, his lawyer said Wednesday, Jan. 25, 2012, without elaborating on the allegations.

NEW YORK — While the city's powerful police commissioner faced questions Friday about a rape allegation against his TV-anchor son, the probe has also put the district attorney in a delicate position.

The Manhattan DA who brought and dropped sex charges against Dominique Strauss-Kahn is now in the thick of another sensitive, highly scrutinized sex-attack investigation, this one involving a relative of a key law enforcement ally. But the new inquiry presents major differences; for one, there have been no arrests.

The commissioner refused to discuss the investigation as he faced the media Friday for the first time since reports surfaced that a woman had accused his son Greg of rape.

"I'm not going to ... with all due respect, answer any questions on this matter," Kelly said at a news conference at police headquarters, saying questions should be addressed to the DA's office. Police have turned the matter over to prosecutors because of the potential conflict of interest in investigating one of the commissioner's sons.

Greg Kelly, the 43-year-old co-host of the local TV morning show "Good Day New York," has vehemently denied doing anything wrong in the episode.

The allegation presents a new high-profile sex-crime probe less than six months after the attempted rape charge against the former International Monetary Fund leader collapsed amid doubt about his accuser's trustworthiness in the biggest case of Cyrus R. Vance Jr.'s two years as DA.

Indeed, the Strauss-Kahn case still looms large enough that Greg Kelly himself queried Vance on-air about it just this Monday. But the two matters are far from parallel, legal experts say.

The DA's office stayed silent about the matter Friday as Mayor Michael Bloomberg praised how Kelly and the police department addressed it and called Vance "a tough, smart guy" who could handle the hot seat.

For a DA in one of the most prominent prosecutor's jobs in the country, "there's always going to be high-profile, complicated cases. There's always going to be second-guessing. He's tough enough to focus on the job," Bloomberg said on "The John Gambling Show with Mayor Mike" on WOR-AM radio.

The woman told police Tuesday she met Greg Kelly for drinks on Oct. 8, they went to her lower Manhattan law office and he assaulted her while she wasn't capable of consenting to sex, a person familiar with the investigation has said.

The woman and Kelly stayed in contact afterward, the person said.

She said she became pregnant from the encounter and had an abortion, according to a law enforcement official. Neither the person nor the official was authorized to speak publicly, and they talked to The Associated Press on condition of anonymity.

At some point, the woman's boyfriend confronted the commissioner in person at a public event, saying Greg Kelly had ruined his girlfriend's life but declining to elaborate on the spot when asked what he meant, according to police spokesman Paul Browne. Browne said the commissioner suggested the boyfriend send him a letter, but the man apparently never did.

Greg Kelly's lawyer, Andrew Lankler, has said the investigation "will prove Mr. Kelly's innocence."

Kelly took time off starting Thursday from his show on local Fox affiliate WNYW-TV, the station said.

Three days before, Vance appeared on the program to talk about the problem of elder abuse. Kelly also questioned him about the case against Strauss-Kahn, who was charged in May with making a hotel maid perform oral sex. The onetime French presidential hopeful has said the encounter was "inappropriate" but not violent.

Prosecutors said they dropped the case in August because the woman had undercut her credibility by lying about her background and changing her account of her actions right after the alleged attack. She says she was truthful about the encounter and is pursuing her claims in a lawsuit.

Some have questioned whether "if she were a more prominent citizen, member of the community, she would not have been subjected to that kind of interrogation," Kelly noted to Vance on the show.

Vance called that a "misimpression and incorrect assessment of the case" and said his office looks at each case carefully.

Even from the few details known so far, the investigation into Kelly has some sharp distinctions from the Strauss-Kahn case, but it may pose just as significant challenges, experts said.

Strauss-Kahn's accuser swiftly reported the alleged attack, prompting an arrest within hours and allowing investigators to gather a sample of the then-International Monetary Fund leader's semen on the woman's work clothes. It's unclear whether they will have any forensic evidence to work with in the investigation into Kelly, or whether his accuser sought medical attention.

Concerned that Strauss-Kahn might flee overseas, prosecutors persuaded a judge initially to hold him without bail. Although Strauss-Kahn was released to house arrest days later, his jailing had forced prosecutors to obtain an indictment because of legal time limits on holding someone without one. The DA's office later faced some criticism that it had rushed to indict before completely investigating, though some legal observers said Strauss-Kahn's foreign ties left prosecutors no choice.

Kelly, on the other hand, hasn't been charged with any crime, so there's no legal deadline looming over prosecutors' investigation.

"There are very significant differences, and that's a justification for (prosecutors) to be more deliberate in how they go about it," said Fordham Law School professor James A. Cohen.

The investigation involves not only the public attention that surrounds any well-connected target, but the added complication of investigating a son of an official who works closely with the DA, noted Pace Law School professor Bennett L. Gershman. He worked in the 1970s for a special state prosecutor appointed to investigate corruption in the criminal justice system.

While the DAs sometimes investigate police officers or their relatives, "this is a special case," Gershman said. "It puts him in a very difficult position."

Indeed, police were defendants in one of Vance's other most prominent and difficult cases: last year's trial of two officers accused of raping a drunken woman they were called to help get home.

The officers were convicted of official misconduct for returning to her apartment without reporting where they were. But they were acquitted of all other charges in a verdict that came less than two weeks after Strauss-Kahn's arrest.

The DA's office has since logged a number of wins in noted sex-crime cases, including a 428-year sentence for a man convicted of sexually attacking five women and a rape conviction and 20-year sentence for a man accused of holding himself out as a worldly French-language journalist to approach women.

While the Kelly investigation may put the DA under pressure again, "it's only comparable to the (Strauss-Kahn and two officers') cases in that it's high-profile," said Linda Fairstein, a former longtime chief sex-crimes prosecutor in Manhattan. "...It'll get done like any other case."

Associated Press writers Samantha Gross and Tom Hays contributed to this report.