The sixth inmate to die inside a New York City jail this year was identified by officials Sunday as a 20-year-old murder suspect.

Emanuel Sullivan, who was in custody on murder and robbery charges from a February incident, was found unresponsive in his bed Saturday afternoon inside the Robert N. Davoren Center on Rikers Island, according to the Department of Correction.

Sources previously told The Post that Sullivan had blood coming from his nose when he was found by a correction officer.

Medical staff immediately arrived, but found no pulse and pronounced Sullivan dead at about 4:25 p.m., the DOC said.

It’s unclear how long he was dead, but his death doesn’t appear to be a suicide, jailhouse sources told The Post.

“The housing area was staffed and all tours were conducted throughout the day,” the DOC said in a news release Sunday.

Sullivan was due back in court this week, records indicate.

“Mr. Sullivan’s passing fills our hearts with grief, as we understand everyone entrusted to our care is someone’s loved one,” DOC Commissioner Louis Molina said in a statement. “Our thoughts and deepest sympathies are with his family and loved ones at this difficult time.”

The death is under investigation.

Sullivan was the third inmate to die at the troubled lockup this month alone.

The last inmate to die in custody was 31-year-old Mary Yehudah, who was found unresponsive in her cell on May 18. She died just 10 days after a 25-year-old inmate hanged himself.

Last year, 16 people died in city lockups — the most since 2013.

The latest comes in the wake damning federal report that found the conditions in the problem-plagued city jail systems to be “severe and potentially life-threatening.”

The #HALTsolidarity Campaign slammed the city for horrible conditions inside the jail.

“Enough is enough. I am so tired and devastated to hear about the death of Emanuel Sullivan,” Victor Pate, co-director of the organization, said in a statement tweeted out. “It is beyond heartbreaking that we continue to hear about the many fully preventable deaths that continue to on Rikers Island. How many more people will die before our public officials will finally start releasing people, stop sending people to these deadly jails, and do something to change the horrible conditions?”