College Football Live details the death of former Nebraska football star Lawrence Phillips, who was found dead Wednesday morning in a California prison. (0:30)

Attorneys representing the family and estate of Lawrence Phillips, the former star running back who was found dead in his prison cell last week, told USA Today Sports that they plan to hire civil rights lawyers to investigate Phillips' death because of a note found in his sock.

Dan Chamberlain, the attorney for Phillips' estate, told USA Today Sports that he is "highly suspicious" because of the discovery of the note, which a coroner found on Phillips.

Phillips, 40, was pronounced dead on Jan. 13 after guards at Kern Valley State Prison in California found him unresponsive in his cell. The Kern County coroner's office ruled that Phillips, who was awaiting a murder trial that could have brought him the death penalty, committed suicide.

But Jesse Whitten and Clayton Campbell, attorneys who represented Phillips in the murder case, told USA Today Sports that the note contained suspicious writing. The attorneys said that the handwriting on the note, which had writing on both sides, did not match the handwriting on previous letters that Phillips had sent them from prison.

"[One side] said, and this to the best of my recollection, 'Did you hear the one about the football player who hung himself from the TV mount in his cell?'" Campbell told USA Today Sports. "And where it said football player, it looked like somebody after the fact put the letter 'X' before 'football,' so it said 'X-football player.'"

Whitten described the other side of the note as saying: "It was something like, 'What's the black person do?' And it ended with like, 'They should just die.'"

Dana Simas, a spokeswoman for the California Department of Corrections and Rehabilitation, did not comment on the note when contacted by USA Today Sports.

Whitten said he saw the note last Friday but has not discussed it with authorities.

"There's just a lot of unanswered questions at this point, and I'm not very confident that the prison is really investigating all of the possibilities," Whitten told USA Today Sports.

Chamberlain also said he is "incredibly skeptical" that Phillips would commit suicide just hours after a preliminary hearing to set up his murder trial.

"All of a sudden he comes back from his court hearing and he kills himself? I find that incredibly skeptical," Chamberlain said. "I'm going to pursue this thing a long way, I can promise you. Because what I've seen so far, it does not seem correct."

Simas told USA Today Sports that Phillips was in single-cell segregated housing, which is checked every 30 minutes, at the time of his death.

"To open a cell would come from [the] control tower in the housing unit," said Simas, who also said that access to the cells is limited only to corrections officers.

Phillips was facing the trial for the alleged murder of his former cellmate Damion Soward, who was found unresponsive in April 2015, in the cell the two men shared. A coroner ruled Soward had been strangled, and Phillips was charged with Soward's murder in September 2015.

Phillips has been in prison since October 2008, and in 2009 he was sentenced to 31 years in prison for separate incidents including assaulting his former girlfriend and driving his car into three teenagers.

Information from The Associated Press was used in this report.