Opening statements began Monday in the trial of Paul Caneiro in New Jersey. 

Caneiro is accused of killing his brother, Keith, sister-in-law Jennifer and their two young children at the family's home eight years ago in Colts Neck, and then setting that home on fire. 

Prosecutors say Caneiro killed the family in 2018 over his brother's plans to remove him from a technology company they shared after money allegedly disappeared from the firm, and for the $1.5 million he'd receive from a life insurance policy if they were all dead. 

Caneiro faces murder, arson, weapons, and theft charges. If convicted, he could spend the rest of his life behind bars. 

"One person, and one person only, committed these crimes," Monmouth County First Assistant Prosecutor Nicole Wallace said. "And that person is sitting right here today." 

Web Extra: Read the Affidavit Part 1 | Part 2

Prosecutors say Caneiro went to his brother's home, shot him in the back and then four more times in the head outside the home. He was found in a pool of blood with a hoodie over his head. His brother's wife was found shot and stabbed, and his 11-year-old son, Jesse, and 8-year-old daughter, Sophia, were stabbed repeatedly. 

"Their daughter Sophia was on the adjacent set of stairs that led up to the second-floor bedrooms, essentially by her mom. And their son Jesse's body was located in the kitchen not too far away," Wallace said. 

Wallace outlined evidence, including blood-stained gloves and the murder weapon, which they say was found at the defendant's house, which was also set on fire. She said the bullets that killed Keith came from a gun found Paul Caneiro's basement. 

Caneiro wiped away tears at times during his court appearance.   

Caneiro has pleaded not guilty, and his defense team says he loved his family and has been wrongly accused. 

"Paul Caneiro did not do this. He did not commit these crimes," defense attorney Monika Mastellone said. "Paul Caneiro is innocent." 

Mastellone said prosecutors never looked into a third brother who also stood to receive money from the life insurance policy. 

"They almost immediately set up a crime scene because it was so obvious," Mastellone said. "They never looked into Cory. They didn't do a single thing to investigate Cory. Not a single thing." 

That brother was not in court, but Paul Caneiro's wife and children were there, listening to testimony. 

"They never even bothered to get Cory Caneiro's DNA," Mastellone said. 

Prosecutors allege Paul Caneiro cut the power to his brother's home, disabling a surveillance system that hours earlier picked up Keith leaving an angry message for Paul.