Police have released a Yale University lab technician whom they held as a "person of interest" in the killing of the graduate student Annie Le.

Raymond Clark was taken into custody last night at his apartment in Middletown, Connecticut, so that police could take DNA samples including saliva, hair and fingernails. Those samples will be compared with physical evidence discovered in the laboratory where Ms Le's body was found on Sunday, the day she had been due to get married.

At the same time a large group of FBI agents arrived to search Mr Clark's apartment, remaining until 8am this morning.

News reports from the scene said that police officers sorted through items on a card table outside the door to the apartment, as Mr Clark's red Ford Mustang was towed away.

James Lewis, chief of police in New Haven, Connecticut, confirmed that Mr Clark had been at the police station but said he had not been arrested.

He would not confirm reports that the technician - who works in the same animal research laboratory where Ms Le disappeared last Tuesday and where her body was found in a wall duct - had scratches on his body and had failed an FBI-administered lie detector test.

The police chief did, however, deny reports that Mr Clark had been hiding from police. "We've known where he was all along," he said. "We've always known where he was at. We've been with him this entire time."

Investigators began staking out Mr Clark's home on Monday, the day after they discovered the body of the 24-year-old pharmacology student in the basement of the lab building. Police also found blood-stained clothing stuffed above a ceiling tile that is believed to belong to the killer.

The New Haven Independent, citing a law enforcement source, said that the suspect, who was also engaged, had an "unrequited love interest" in the student.

Mr Clark shares his apartment with his girlfriend, Jennifer Hromadka, whom he planned to marry in December 2011, according to the couple's incomplete wedding web site.

On the site, Ms Hromadka describes her boyfriend as “a bit naive, doesn’t always use the best judgement, definitly [sic] is not the best judge of character but, he is a good guy”.

She adds: "He has a big heart and tries to see the best in people ALL THE TIME! He thinks everyone deserves a second chance.”

Mr Clark moved to Middletown, about 32 kms (20 miles) from New Haven six months ago, according to Taylor Goodwin, 16, a former neighbour. "I never really talked to him much, he was just some guy," he said.

The Le family issued a statement through a family friend, the Reverend Dennis Smith, thanking friends and the Yale community for their support . "The entire Yale community as well as our extended families and friends have been very supportive, helpful and caring," said the Reverend Smith, speaking for the family. "Our loss would have been immeasurably more difficult to cope with without their support."

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