A Connecticut police chief says authorities may never know the motive for the killing of a Yale University graduate student whose body was found hidden behind a wall.

PHOTOS: Yale Graduate Student Murdered

New Haven police Chief James Lewis told local television stations Friday the only person who knows the reason for the murder of Annie Le is the man charged with the crime, Raymond Clark III.

The Yale lab technician was arrested Thursday, a day after police 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 law enforcement source who talked to The Associated Press on the condition of anonymity said Thursday co-workers called Clark a "control freak." Authorities are investigating whether that attitude might have set off a clash between Clark and Le.