Calling Darryl Littlejohn the “prime suspect” in the rape and murder of graduate student Imette St. Guillen, Police Commissioner Raymond Kelly announced that blood found on plastic ties used to bind the victim belonged to Littlejohn.

“As a result of this and other evidence, Littlejohn is the prime suspect in this case and his indictment will be sought for the murder of Imette St. Guillen,” Mr. Kelly said yesterday at a press conference to announce the “break in the case.”

Mr. Kelly said there is other evidence that could be used to charge Littlejohn. Witnesses said St. Guillen left the Falls bar with Littlejohn, a bouncer at the bar, and cellular telephone records from the day of the murder place him in close proximity to the desolate area in East New York where the woman’s body was dumped, Mr. Kelly said.

“This is a very significant development,” Mr. Kelly said. “We talk about DNA and we’re talking about the certainty of one in a trillion. So it’s a very important piece of evidence.”

The blood tests were administered at the DNA laboratory of the medical examiner’s office, a spokeswoman, Ellen Borakove, said. The DNA evidence and other findings will be presented before a Brooklyn grand jury this week, Mr. Kelly said.

“There’s a lot more forensic work to be done in this case,” Mr. Kelly said.

St. Guillen, 24, was at the Falls in SoHo at about 4 a.m. on February 25. Police initially believed she had left the bar alone. News accounts have reported that St. Guillen appeared to be so inebriated that she was asked to leave the bar, which is owned by the Dorrians, the family that also runs Dorrian’s Red Hand on the Upper East Side. Her alleged escort was Littlejohn.

The Falls was the last place police said the John Jay College of Criminal Justice student was seen alive before her body turned up that night. St. Guillen had been sexually abused and bound. Her naked body was wrapped in a comforter and abandoned in a desolate area off the Belt Parkway.

The medical examiner’s office ruled the woman’s death a homicide by asphyxia.

Although he has not been arrested or charged in the slaying, Littlejohn – who has used a host of aliases – is being held at Rikers Island on a parole violation for breaking curfew in a separate case. He was supposed to be home between 9 p.m. and 7 a.m. He had a day job at a mortgage company that the Division of Parole had approved, a spokesman for the division, Scott Steinhardt, said.

In addition to the evidence linking Littlejohn, 41, to the St. Guillen case, forensic results have surfaced connecting the ex-convict to other open sexual assault cases, Mr. Kelly said. Those findings also will be used to mount a case before the grand jury, Mr. Kelly said.

Before the press conference yesterday, Mr. Kelly said that detectives had consulted prosecutors, as they had throughout the course of the investigation. A spokesman for the Brooklyn district attorney’s office, Jonah Bruno, said he could not comment on the case.

Police had been eyeing Littlejohn in the high-profile case but had not proclaimed him the main suspect until yesterday. Investigators suffered a setback last week when at least one sexual assault victim failed to identify Littlejohn in a lineup.

An assistant district attorney, who requested anonymity because he is not in a position to discuss the case publicly, said, “It’s not uncommon for people not to be able to identify a suspect in a lineup.”

Littlejohn’s criminal career dates back to age 16. He pleaded guilty to first-degree robbery in December 1980, the Manhattan district attorney’s office said. He was sentenced to 3 1/3 to 10 years in prison. His most recent conviction was for robbery and criminal use of a firearm. He was conditionally released on parole in July 2004 and was supposed to be under supervision until November 2006.

The case of St. Guillen has prompted outrage in the city and spurred extensive press coverage.

John Jay College, where St. Guillen was a criminal justice graduate student, established a college scholarship in her memory. A memorial notebook resting on a table inside the school lobby was filled with messages from students and visitors passing by.