CSI expert was key to arrest in death

? From the moment the NYPD crime lab received the physical evidence recovered from the body of slain graduate student Imette St. Guillen, top forensic expert Nicholas Petraco was on the case.

In fact, the grand jury testimony of Petraco, a retired NYPD criminologist who now works as a consultant to the department, was key to charging bouncer Darryl Littlejohn with her murder, the New York Daily News has learned.

Even before police searched Littlejohn’s Queens apartment on March 6, Petraco and a team of crime lab technicians had spent days examining “trace transfer evidence” from the tape and blanket found on St. Guillen’s body.

At a news conference to announce Littlejohn’s indictment, Brooklyn Dist. Atty. Charles Hynes said forensic evidence played an unprecedented role in linking Littlejohn, a 41-year-old ex-con, to the murder of St. Guillen, 24, a student of CUNY’s John Jay College of Criminal Justice.

“There will be a course on this in law schools,” Hynes said.