The body was identified as Roosevelt Rene, 25, a Jenkins family friend who had been living at the house, according to the Bergen County Prosecutor's Office.
The office announced Wednesday that William Jenkins was in custody, adding that the investigation is ongoing. On Thursday, New York State Police said in a statement that Jenkins is in the Ontario County Jail for a parole violation and is awaiting extradition to New Jersey.
According to New York state department of corrections records, William Jenkins was arrested on drug charges in 2006 and again in 2011. He was paroled from prison in July 2016.
Janoris Jenkins was not at home when the body was discovered and has been in Florida since the completion of Giants minicamp two weeks ago, sources said. Jenkins has been advised by attorneys to remain in Florida, sources said.
The Giants said that they "are aware of and monitoring the situation."
Information from ESPN's Josina Anderson and Jordan Raanan, and The Associated Press was used in this report.