NEW YORK - US officials confirmed Wednesday that a young Yale scientist was strangled before being stuffed in a wall, as the police net closed around a lab technician at the Ivy League university.

"The cause of death was traumatic asphyxiation due to neck compression," a spokeswoman for the Connecticut state medical examiner told AFP, announcing the results of the autopsy on student Annie Le, 24.

Le's body was found Sunday, the day she had been due to marry and five days after she disappeared in the carefully guarded facility, where experiments are performed on animals.

No one has been charged, but the focus was intensifying on lab technician Raymond Clark, also 24.

FBI agents and local police poured late Tuesday into his Middletown, Connecticut, residence and took him away to obtain DNA samples, which will be checked against evidence found at the scene.

"He was released at three o'clock this morning after he complied with our search warrant," said Jessica Mayorga, spokeswoman for police in New Haven, home of Yale.

"If we find a reason after we go through the evidence to bring him back in we will, but we can't hold him now," she told AFP.

Clark has not been charged, but remains a "person of interest." Police were initially mystified by Le's vanishing inside the strictly controlled laboratory. Repeated searches failed to discover the body until a dog trained in sniffing for cadavers found her remains stuffed in a wall cavity.

Police are also examining hundreds of hours of security camera footage and questioning every person who was present in the building. Some 150 pieces of physical evidence were collected at the crime scene.

The hunt for the killer at one of the country's most prestigious universities stirred fevered interest in the US media.

The New York Daily News reported that Clark had been upset about Le's treatment of mice used in experiments, and that the petite Vietnamese-American grad student had promised to follow protocols more closely.

"Investigators wonder if Clark was not satisfied, if resentment suddenly flared to rage, if as crazy as it may seem this was a case of mice and murder," Daily News columnist Michael Daly wrote.

Local media reports said that Clark had failed a lie-detector test and also had scratches on his arm.

But police went out of their way to be cautious, insisting that Clark was merely a focus of the enquiry.

"Clark was removed from his residence in accordance with a second search and seizure warrant and transported to a law enforcement facility for the purpose of seizing potential evidence relative to the homicide investigation," police said in a statement following the raid late Tuesday.

"Clark has not been charged in the death of Annie Le and will be released upon his compliance with the search and seizure warrant." However, FBI investigators shadowed Clark for days, with 15 agents tailing him at a local fair over the weekend, ABC television news reported.