Authorities suspect the brother and business partner of a man who was killed along with his family in fire at a New Jersey mansion was behind their deaths.

Paul Caneiro is being investigated for his role in the fire on Tuesday afternoon that police are investigating as a “multiple homicide and arson case," the Monmouth County Sheriff's Office told The Daily Beast. Found dead at the residence in nearby Colts Neck were Kevin Caneiro, 50, his wife, Jennifer, 45, and their two kids under age 10, neighbors said.

Authorities said they believe there is a connection between the two fires, though they did not speculate on a motive.

Caneiro was arrested and booked into jail Wednesday morning in connection with another suspicious fire at his own home early Tuesday morning, authorities said. Caneiro was charged with one count of second-degree aggravated arson for the blaze.

According to an arrest warrant obtained by The Daily Beast, Caneiro, 52, "purposely or knowingly" used gasoline to start a fire at his Ocean township home around 5 a.m Tuesday while his wife and two daughters were still inside.

Firefighters responded to a report of fire in Colts Neck, a 20-minute drive from Ocean Township, around 12:30 p.m.

A Colts Neck neighbor described the Tuesday afternoon fire as “horrific,” saying the blaze was still raging hours after firefighters responded the scene.

“The fire seemed to get worse as the firemen tried to bring it under control. Even this morning there is still a gray smoke outside. It’s so terrible, that poor family,” the neighbor, who wished to remain anonymous, told The Daily Beast. “I hope police get some justice for the family.”

Keith Caneiro was discovered outside with a gunshot wound that was not self-inflicted. Jennifer Caneiro and the couple's children appeared to have been stabbed and were found “severely burned” inside the house, said Monmouth County Prosecutor Christopher J. Gramiccioni in a press conference on Wednesday,

A medical examiner is still investigating how the four people died, Gramiccioni confirmed.

Hours after firefighters were able to contain the blaze, investigators discovered “several gas cans in the rear of the house,” Gramiccioni said.

“It’s important to emphasize that we have no reason to believe that anyone in the community is in any danger at this time,” he added.

Keith Caneiro was the founder and chief executive officer of Square One, a technology-services consulting firm in Asbury Park, New Jersey. On the company website, his brother Paul is listed as vice president. The brothers also appear to have worked together at Jay-Martin Consulting, and they shared an address in Staten Island for more than a decade, records show.

The earlier fire at Paul Carneiro's house, a single-family home on Tilton Drive in suburban Ocean Township, awoke neighbors as firefighters struggled to put out the flames on the roof. It is not immediately clear if anyone was injured in the fire, the arrest warrant states.

That home is owned by Susan and Paul Caneiro, public records confirm.

Kevin Harrington, a neighbor who lives across the street from the Caneiro home, said he saw some family members sitting in a car outside their home early Tuesday morning.

“They have always been great people to me and my family,” Harrington told The Daily Beast. “This whole situation is pretty shocking stuff and the fire was really scary to see up close.”

Another neighbor, who wished to remain anonymous, confirmed to The Daily Beast that Paul and Susan were at home at the time of the fire and were sitting outside while firefighters worked until about noon, then they left in their car.

“Paul said it must’ve been a gas leak and he was crying. Susan was devastated,” she said.