Raymond Clark III, the man charged in the murder of Yale graduate student Annie Le, pleaded guilty to murder and attempted sexual assault.
Clark entered the plea on Thursday under an agreement that calls for a 44-year-sentence.
Le, a 24-year-old Placerville, Calif., vanished on Sept. 8, 2009, from the Yale medical school research building where she and Clark worked.
Clark was responsible for caring for lab mice, cleaning floors and cages. One official told the Associated Press that Clark's Yale co-workers told police he was a "control freak," fastidious and territorial about the mice whose cages he cleaned, even with scientists and doctoral students at the Ivy League school.
Le's body was found on Sept. 13, the Sunday she was to marry Jonathan Widawsky, a Columbia University student. Her body was in a wall of the Yale lab building.
"Ray has wanted to reach out and express his remorse of having caused this horrible tragedy. However, Ray and my family have followed the advice of his attorneys and not made any comments while the case was pending," Ray Clark II said. "As a parent, it is very hard to think that your child could commit such a horrible crime."
Le's family was not in court but plans to attend the sentencing, which is scheduled for May 20.
Thursday was the first time there was any public mention of attempted sexual assault.
Prosecutors said there were traces of semen found on Le's panties and Clark's scrubs.
Clark had been charged with murder and felony murder, each carrying a possible sentence of 25 to 60 years.