A spokesman for New Haven police, who have been extraordinarily tight-lipped during the investigation, did not immediately return a call seeking comment.
Police said earlier Tuesday that they had questioned 150 people in connection with the death of Le, who vanished Sept. 8 from a Yale research building. Her body was found Sunday, on what would have been her wedding day, stuffed behind a wall in a basement laboratory. They said they did not expect to make an arrest Tuesday.
State prosecutors also blocked the release of autopsy results in Le's death on Tuesday. The chief state medical examiner's office ruled the death a homicide Monday but have yet to say the manner in which Le died.
State's Attorney Michael Dearington did not return a call seeking comment on why his office requested that the autopsy results be delayed.
Authorities were keeping watch on some of Le's co-workers and have descended in large numbers this week on the home of a Yale animal research technician who lives in the Wharfside Commons apartment complex in Middletown.
An official parked outside complex, about 20 miles away near Hartford, wouldn't confirm whether police were there to investigate the Le killing, but public records show the technician lives in a first-floor apartment. A man answering the door Tuesday said the technician wasn't at home and closed the door.
Neighbors said authorities in unmarked cars arrived Monday afternoon and frequently follow and pull over drivers in the complex. New Haven police would not comment on the efforts there.
Police are analyzing what they call "a large amount" of physical evidence but have not gone into detail.
At a meeting of medical school students and teachers Monday, Yale president Richard Levin said police have narrowed the number of potential suspects to a very small pool because building security systems recorded who entered the building and what times they entered, the Yale Daily News reported Tuesday. The appropriate people are being monitored, he said.
Yale spokesman Tom Conroy said he couldn't confirm the report.
The killing took place in a heavily secured building accessible only to students and university employees. It was the first killing at Yale in a decade.
Hundreds of students attended a Monday night prayer vigil where Le's roommate, Natalie Powers, recalled her friend as tenacious, caring and "tougher than you'd think by just looking at her."
"That this horrible tragedy happened at all is incomprehensible," she said. "That it happened to her, I think is infinitely more so. It seems completely senseless."
Police found Le's body about 5 p.m. Sunday, the day she was to marry Columbia University graduate student Jonathan Widawsky, lovingly referred to on her Facebook page as "my best friend." The couple met as undergraduates at the University of Rochester and were eagerly awaiting their planned wedding on Long Island.
Police have said Widawsky is not a suspect and has helped detectives in their investigation.
Le was part of a research team headed by her faculty adviser, Anton Bennett. According to its Web site, the Bennett Laboratory was involved in enzyme research that could have implications in cancer, diabetes and muscular dystrophy. Bennett declined to comment Monday on the lab or Le's involvement with it.
The Yale building where Le's body was found is part of the university medical school complex about a mile from Yale's main campus. It is accessible to Yale personnel with identification cards. Some 75 video surveillance cameras monitor all doorways.
Her body was found in the basement in the wall chase - a deep recess where utilities and cables run between floors. The basement houses rodents, mostly mice, used for scientific testing by multiple Yale researchers, Alpern said.
The death is the first killing at Yale since the unsolved December 1998 death of student Suzanne Jovin. The popular 21-year-old senior was stabbed 17 times in New Haven's East Rock neighborhood, about 2 miles from campus.
Haigh reported from Hartford, Conn. Associated Press writers Dave Collins and Pat Eaton-Robb in New Haven, Conn.; Frank Eltman in Huntington, N.Y.; Juliet Williams in Placerville, Calif.; and AP news researcher Rhonda Shafner in New York also contributed to this report.