Paul Caneiro was found guilty of killing his brother Keith, and his brother's wife Jennifer, and their two children Jesse and Sophia.
In addition to the murder counts, Caneiro was also found guilty for several other charges, including two counts of aggravated arson, possession of firearm for unlawful purpose, possession of knife for unlawful purpose, theft, misapplication of entrusted property and hindering ones own apprehension or prosecution.
The jury reached the verdict on Friday, after just a few hours of deliberations.
The trial for the November 2018 murders began last month.
Keith was found fatally shot outside his Colts Neck home, his wife, Jennifer shot and stabbed inside along with the couple's kids who had also been stabbed.
Prosecutors claim that after the murders, Paul set his own house on fire in Ocean Township, New Jersey, as a way to cover up the crimes by burning evidence and making authorities believe he too was a victim.
Hours later, authorities learned about the earlier murders of Paul's brother and family. That's when they started to investigate Paul as a possible suspect.
Prosecutors say the motive for the cold-blooded slayings was money, and was part of an insurance fraud scheme. The brothers owned two businesses together in Asbury Park.
Part of the defense effort to raise reasonable doubt was that police never investigated another brother in the family.
Caneiro will face a maximum of multiple life sentences without parole, and is scheduled to be sentenced in May.
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