Former NFL player Aaron Hernandez and defense attorney Charles Rankin wait in the courtroom during the jury deliberation in his murder trial at the Bristol County Superior Court in Fall River, Massachusetts, April 10, 2015. REUTERS/CJ Gunther/Pool

By Scott Malone

BOSTON (Reuters) - Massachusetts prosecutors said on Monday that an anonymous caller, who told lawyers for former NFL star Aaron Hernandez that one of the jurors who found him guilty of murder should have been disqualified, had a sexual relationship with the athlete.

The former New England Patriots tight end was found guilty in April of murdering an acquaintance, Odin Lloyd, in 2013, and sentenced to life in prison at the end of the first of two murder trials he will face this year.

Following his conviction, his lawyers told the court they had been called by a person who gave her name only as "Katy," who they said claimed to have known one of the jurors who found Hernandez guilty and to have also known that the juror was aware that Hernandez was also charged with a 2012 double homicide.

The judge in Hernandez's first trial of the year had ruled that jurors in the case, tried at Bristol County Superior Court in Fall River, Massachusetts, not be told that Hernandez would also be tried in Boston for allegedly murdering two Cape Verdean nationals outside a nightclub.

Proof that a juror in the case had lied about his or her knowledge of Hernandez or had discussed the case outside of court could be grounds for the conviction to be overturned. Defense lawyers had asked the judge in the case to call the anonymous witness into court to be questioned under oath.

Prosecutors said in a court filing on Monday they had learned that the person, whose name they said is not "Katy" but which they did not disclose, had "an ongoing sexually explicit relationship with the defendant prior to and during the trial."

They contended that the person had believed her relationship with Hernandez would continue after his trial if he were found innocent.

Hernandez' lawyers could not be reached for immediate comment.

The Patriots cut Hernandez, a rising star with a $41 million contract, hours after his arrest on June 26, 2013, nine days after a teenage jogger found Lloyd's body and Hernandez was charged in his killing.

He was later charged with fatally shooting Daniel Abreu and Safirdo Furtado outside a nightclub after one of them spilled a drink.

Hernandez is due to stand trial for those murders, as well as charges of trying to intimidate a witness by shooting him in the face, later this year.

(Editing by Eric Walsh)