Lawrence Phillips Murder Case -- Victim May Have Been Sexually Assaulted (Update)

11:42 AM PT -- The Kern County D.A.'s office tells us Phillips has NOT been charged with sexual assault and there is no pending sexual case against him.

Translation -- the sexual assault kit must have not shown any signs of a sexual assault.

Another shocking twist in the Lawrence Phillips murder case ... TMZ Sports has learned officials believe the victim may have been sexually assaulted around the time he was killed.

The former NFL running back has already been charged with 1st degree murder in the April 11th death of his cellmate at Kern Valley State Prison ... where Phillips was already serving time for a plethora of other crimes.

But an incident report obtained by TMZ Sports shows officials administered a sexual assault kit on the victim in the days following the murder.

We spoke with officials involved in the murder investigation who tell us a sexual assault kit is NOT a standard operating procedure with murder victims at KVSP -- "There would have to be a reason to believe [a sexual assault occurred]. Some evidence or something else."

It's unclear what the sexual assault kit turned up -- or if prosecutors plan to charge Phillips with a sex crime.