Fotis Doulos was found dead earlier at his home in Connecticut, USA, according to American media.
Doulos had been charged with abducting and killing Jennifer's estranged husband.
According to the New York Times, the first signs indicate suicide. His lawyer confirmed his death.
The case of Fotis Doulos has occupied the media around the world.
Doulos had been charged with abducting and killing his estranged wife, who disappeared on May 24.
He was arrested and charged, but his body was never found.
The police investigation indicated that Jennifer had been murdered by her husband.
The first indication was the blood stains on her car, but also on the seat of a vehicle that her estranged husband had borrowed from an employee on the day of his disappearance.
At least twenty items with genetic material were also found in trash cans - about 120 miles (XNUMX km) from her Connecticut home.
At that time, the couple's legal dispute over the custody of their five children was ongoing.
When Jennifer filed for child custody in 2017, she said she felt she was in danger from her estranged husband.