One of the suspects in the brutal 2010 killing of a University of Louisiana at Lafayette student dodged a possible murder conviction and life sentence Monday by pleading guilty to a lesser charge.

As part of the plea deal, Ian Trahan agreed to help police identify a third suspect known only as “Black,” Trahan’s attorney said.

Trahan, 25, pleaded guilty to manslaughter in state District Judge Marilyn Castle’s court early Monday, the day his trial on second-degree murder and attempted second-degree murder was to start.

Trahan and 27-year-old Wayland Guillory faced identical charges in the Oct. 28, 2010, beatings of Kenneth Donnelly Jr. and Donnelly’s roommate, Rufus Fells.

Donnelly, who was 20, died from his injuries while Fells survived but suffered permanent damage. Both were from Alexandria, where Fells returned to recuperate. Medical reviews showed the pair had been beaten with a metal object, and authorities said the attack was connected to an alleged drug deal.

According to Trahan’s plea form, he will spend no more than 20 years in prison for the manslaughter conviction, a crime that according to Louisiana statutes carries a maximum sentence of 40 years in prison at hard labor.

Judge Castle will sentence Trahan at 9 a.m. July 9.

The prosecutor in the case Monday revealed few details about Trahan’s plea agreement or about detectives’ work in the case. Although the plea form was released by officials, the document spelling out the full plea agreement has been ordered sealed until Trahan’s sentencing in July.

“We don’t want to go into any details about it because it could jeopardize an ongoing investigation,” said Assistant District Attorney Janet Perrodin, who took over the case in early 2015.

Trahan’s attorney, Thomas Guilbeau, said Monday that Trahan’s agreement with the Lafayette Parish District Attorney’s Office stipulates he’ll receive a sentence of 15 years in prison if he’s truthful with investigators and helps identify a third suspect in the case.

Guilbeau identified the third suspect only as “Black,” who Guilbeau said might have been standing watch outside the victims’ home when they were beaten. Police and prosecutors have never publicly stated there might be a third suspect.

Guilbeau said the agreement also calls for his client to receive a 20-year sentence if he’s untruthful with detectives in their quest to find the third man.

Guillory, of Lafayette, pleaded guilty to manslaughter in January. His agreement with the District Attorney’s Office also calls for a prison sentence far shorter than the zero to 40-year range allowed by Louisiana sentencing laws. Guillory’s sentence will be capped at 10 years if he provides useful information to detectives about the case.

Trahan, of Youngsville, this week was temporarily incarcerated in the Lafayette Parish Correctional Center. He was transported to Lafayette from the Louisiana State Penitentiary at Angola, where he is serving a five-year sentence for drug possession. That conviction is unrelated to the 2010 killing.

Donnelly and Fells were attacked in their rented home at 302 McKinley St., located near a row of bars that cater to college students called The Strip.

According to a police affidavit, Trahan called Fells from a cellphone to buy marijuana early that October morning.

The call was the last one placed to Fells’ cellphone before the attack.