NEW HAVEN, Connecticut (CNN) -- Yale University graduate student Annie Le, whose body was found in the basement wall of an off-campus medical research building, was strangled, a spokesman for the Connecticut medical examiner's office said Wednesday.
The body of Yale University student Annie Le, 24, was found on the day she was to have been married.
The cause of death was "traumatic asphyxia due to neck compression," the spokesman said. The office would not release the spokesman's name.
Le, 24, a pharmacology student, was last seen alive September 8, the day she appeared in a surveillance video entering a four-story lab at 10 Amistad St., about 10 blocks from the main campus.
Her body was found Sunday, on what was to have been her wedding day. No one has been arrested or charged in her death.
A Yale employee was released around 3 a.m. Wednesday after he was detained so officers could collect DNA from him, New Haven Police Chief James Lewis said. Watch panelists weigh in on Le's slaying »
Police took Raymond Clark, 24, into custody after obtaining a search warrant for his home and a warrant to collect DNA, said Lewis, describing Clark as cooperative. Watch how police briefly detained the lab tech »
Clark could have been arrested if he declined to provide DNA samples, but he was released after complying, New Haven city spokeswoman Jessica Mayorga.
Two other search warrants also were executed Wednesday -- one on property belonging to Clark that was not named in the first warrant, and a second for Clark's vehicle, which was being processed Wednesday evening, Lewis said.
Asked if police have Clark under surveillance, Lewis said, "We know where Mr. Clark is at all times." But, he added, there are others who police are monitoring "all the time." Watch police discuss the investigation »
The only search warrants executed in the case have been those involving Clark, he said, but other people are being investigated.
He said Clark is a technician who does "custodial-type" work at the building. He answered police's questions for a while at first, but later retained an attorney and stopped, Lewis said.
"We have no authority to detain him in any way at this time."
Lewis said Clark and Le worked in the same building and passed in the hallway, but refused to comment further on whether they knew each other.
Investigators have collected about 250 pieces of evidence, Lewis said.
"If we have one match on a person we know was at that location," police will seek an arrest warrant, he said. Lewis earlier said police had reviewed about 700 hours of video and interviewed more than 150 people, some more than once.
A senior police official disputed Yale University President Richard Levin's claims that the suspect pool would be a "limited number" of people who had been in the basement the day Le disappeared.
"We know everyone that was in the basement ... and we passed that on to police," Levin said. "There is an abundance of evidence."
But the police official, whom CNN is not naming because of the sensitive nature of the ongoing investigation, said investigators believe dozens of people could have had access to that area of the building. Watch a timeline leading up to Le's death »
The police official said investigators were unlikely to make any arrest until DNA evidence is returned from analysis and that the investigation could take days or weeks.
Authorities have not released information on what DNA evidence may have been found, although investigators said earlier that bloody clothing was found hidden above tiles in a drop ceiling in another part of the building.
Police have not described the clothes that were found, nor said to whom they might have belonged. Teams of investigators at a Connecticut State Police lab worked through the weekend processing and examining the bloodstained garments.
But Thomas Kaplan, editor in chief of the Yale Daily News, said a Yale police official told the college paper that the clothes were not what Le was wearing when she entered the building.
Lewis said Wednesday that processing of the building was nearing completion and police would likely clear it Thursday morning.
On Sunday, New Haven Police spokesman Joe Avery said Le's killing was not a random act, but would not elaborate. Watch a report on the police saying the killing was no random act »
Le was to have been married Sunday on New York's Long Island to Jonathan Widawsky, a Columbia University graduate student.
Le was from Placerville, California, and seemed to have been aware of the risks of crime in a university town. In February, she compared crime and safety at Yale with other Ivy League schools for a piece for B magazine, published by the medical school.
Among the tips she offered: Keep a minimum amount on your person. When she walked over to the research building last week, she left her purse, credit cards and cell phone in her office.
CNN's Tom Foreman, Mary Snow and Shirley Zilberstein contributed to this report.
All About New Haven • Yale University • Connecticut
Yale University in New Haven, Connecticut 
A graduate student attending Yale University who went missing five days before her planned wedding was found dead on Sunday, police said.

Annie Le, an American doctoral student seeking a degree in medicine, went missing on September 8, five days before her planned wedding. Investigators reviewed footage from the security cameras of 10 Amistad, the building where Le last entered, and found no evidence that she had left. Police scouring the building found a body, later identified as Le's, hidden in a wall. Earlier, police had found bloody clothes in the ceiling, which they think belonged to the killer.

According to the medical examiner, Le had been strangled.

Le was set to marry Jonathan Widawsky, a graduate student studying physics at Columbia University.

Police believe that there was a motive, and that the slaying was not random. A lab technician, who was labeled a "person of interest" by police, had failed a polygraph and had defensive wounds on his chest, was detained and later released. However, no arrests have been made in connections with the homicide, according to a police spokesman.

In December 1998, Suzanne Jovin was found murdered on the Yale campus.