New Haven, Conn. ? Police may never know the motive for the killing of a Yale University graduate student whose body was found hidden behind a wall on what should have been her wedding day, the police chief said Friday.

“The only person who knows the motive is the suspect,” Chief James Lewis told The Associated Press in a telephone interview. “It’s true in many cases. You never know absolutely unless the person confesses, and in this case it’s too early to tell.”

Raymond Clark III, a technician in the lab where Annie Le conducted research, was arrested Thursday, a day after authorities took DNA samples from him to compare with evidence from the crime scene. His bond was set at $3 million, and he did not enter a plea.

A telephone message seeking comment from the public defenders’ office, which is representing Clark, was not immediately returned Friday.

Lewis said Friday that no further arrests were expected, but investigators were sifting through hundreds of pieces of evidence. He said police had trailed other people before they zeroed in on Clark as a suspect.

A law enforcement official who talked to the AP on condition of anonymity because the investigation was ongoing and many details remained sealed said Thursday that co-workers called Clark a “control freak” who was territorial about the mice whose cages he cleaned. Authorities are investigating whether that attitude might have set off a clash between Clark and Le.

Clark tried to hide evidence even as investigators worked in the basement lab around him, authorities said, then coolly played a softball game on the day Le’s body was found stuffed inside a nearby wall.

An investigator observed Clark trying to hide cleaning equipment that contained blood splatters as teams probed the disappearance of Le, who was 24, according to a law enforcement official familiar with the investigation who spoke to The Hartford Courant.