The brother of the man found dead along with his wife and two kids at his burning New Jersey mansion has been arrested.

New York Post reports Paul Caneiro, 51, the brother of Keith Caneiro, 50, was charged at the Monmouth County jail in New Jersey on a charge of aggravated arson, the Monmouth County Prosecutor's Office said.

Paul Caneiro, who is business partners with his brother, Keith, at the New Jersey-based tech firm Square One, was charged in connection with the blaze that tore through his own New jersey home earlier in the day, officials said.

According to a criminal complaint, Paul Caneiro set the fire to his home "by using gasoline and igniting the gasoline causing the residence to catch fire while his wife and two daughters were inside."

More than seven hours after the fire erupted inside of Paul's home, a suspicious blaze broke out at around 12.30pm (4.30am AEDT) inside of Keith's sprawling home in Colts Neck, New Jersey, roughly 20 kilometres away.

"Unfortunately, they were burned severely as a result of the fire they were exposed to," Monmouth County Prosecutor Christopher Gramiccioni had said at a press conference.

Officials believe that the fires are connected, according to WABC.

Paul Caneiro has not been charged with the murders of his brother and family, but police told the Daily Mail other charges were expected.

There were reports that Keith Caneiro has been shot in the back and head, while his wife and children, Sophia and Jesse, had been stabbed, before being burned.

A neighbour of Paul Caneiro's told NJ.com that the accused arsonist was visibly upset hours after the fire at his home was extinguished.

"He said, 'It must've been a gas leak.' He has tears in his eyes. [His wife] Susan was devastated," the neighbour said. "He said, 'I'm in complete shock. I can't believe this is happening to me.'"

This story was originally published in the New York Post and is reprinted with permission.