Patrick Latko of Wenonah was also found guilty of weapons charges stemming from the November 2011 stabbing deaths of 29-year-old Ryan Patterson and Patterson's 64-year-old mother, Diana.
Investigators say Ryan Patterson was stabbed more than 20 times and his mom was stabbed more than 10 times during an attack inside their Hammonton home.
Atlantic County prosecutors say Latko was jealous of Ryan Patterson because he had been spending time with his ex-girlfriend Holly.
Latko was arrested a few weeks after the bodies were found.
Ryan Paterson was a well-known rider on the South Jersey amateur motocross circuit.