Janoris Jenkins' Brother William Jenkins Charged with Manslaughter

The brother of NY Giants star Janoris Jenkins has been charged with aggravated manslaughter in the death of a man found in the basement of JJ's New Jersey home ... officials say.

TMZ Sports broke the story ... William Jenkins was taken into custody early Tuesday morning on an unrelated parole warrant violation.

But now, officials clearly believe that, before they arrested Jenkins, he killed Roosevelt Rene ... the man discovered at Janoris' home.

Rene's body was not found until roughly 9 hours after William was arrested. But, once they started investigating ... they believe they found enough evidence to connect William to the killing.

The Bergen County Prosecutor’s Office says the investigation is ongoing and notes that the charges are "merely accusations. Defendant presumed innocent."