5:21 PM PT -- Officials have identified the victim as 25-year-old Roosevelt Rene -- a friend of Janoris.

Rene was a music producer who had been living at the home.

1:52 PM PT --The Bergen County Prosecutor’s Office tells TMZ Sports ... the dead body is a man, but he's NOT the owner of the house.

Officials will not release the identity until next of kin have been notified.

"The investigation is ongoing, and additional information will be provided when it is available and appropriate for release."

A dead body was found at the New Jersey home of NY Giants star Janoris Jenkins on Tuesday and now the Major Crimes Unit is investigating ... TMZ Sports has learned.

First off, we're told Janoris was out of the state when the body was discovered early Tuesday morning -- but sources connected to the NFL player tell us his camp is aware of the situation.

We don't know if cops have identified a suspect or even have a working theory on how the person died.

Sources tell us the body was discovered in the basement by a worker at the house. Law enforcement officers in Bergen County raced to the scene. We're told the coroner showed up a short time later.

The identity of the victim is unclear -- we know investigators are actively working the case.

One source connected to Jenkins says the NFL player has been in Florida and was not at the home when cops arrived.

We've reached out to JJ's reps for comment -- but, so far, no word back.