Keith Caneiro and his older brother, Paul, had been arguing over finances for months.

Tens of thousands of dollars had gone mysteriously missing from the two New Jersey companies they co-owned, and Keith came to suspect his sibling was responsible for the lost funds. Finally, on Nov. 19, he emailed two coworkers, telling them he’d decided to stop paying his brother’s salary.

“Keith indicated that he wanted to sell one of the businesses” and that “he was frustrated with Paul and the amount of money Paul spent from their business accounts,” a criminal complaint filed Monday said.

Keith added in the email that he would be “discontinuing payments” to Paul and his wife until he could “locate the money,” according to the court docs.

One day later, 50-year-old Keith was found fatally shot outside his house. His wife, 45-year-old Jennifer Caneiro, their 11-year-old son, Jesse, and 8-year-old daughter, Sophia, were found stabbed to death inside the home.

On Monday, a Monmouth County grand jury returned a 16-count indictment against Paul Caneiro, 52, alleging he murdered his brother and his family on Nov. 20 before burning down their Colts Neck mansion to cover up the crime. According to the court papers, the hideous crime occurred after the elder Caneiro stole about $78,180 from Square One, the technology firm in which his brother owned a 90 percent stake.

The charges have now doubled against the quadruple-homicide suspect since he was originally arrested in November. This latest indictment, which provides new details of Caneiro’s alleged crime, now charges the 52-year-old with four counts of first-degree murder, two counts of felony murder, two counts of second-degree aggravated arson and four counts of possession of a weapon.

Caneiro was also charged Monday with one count of theft, one count of misapplication of entrusted property, and two counts of hindering his own apprehension. If convicted, the father-of-two faces multiple life sentences without parole.

Prosecutors allege that Caneiro, in an “elaborate ruse to cover his tracks,” used gasoline to set fire to his own house in Ocean Township while his wife and two children were still inside, after setting his brother’s basement ablaze.

Surveillance video from Paul Carneiro’s home shows him walking into the garage around 1:30 a.m. to shut down the video camera, about three hours before authorities respond to the scene, the indictment says. One camera located outside his house caught him leaving around 2 a.m.

In an interview with police, the 52-year-old said he “didn’t recall” why he turned off the numerous video cameras, but insisted they were “causing his Wifi” to slow down.

Police responded to the younger Carneiro’s Colts Neck home at around 12:40 p.m. on Nov. 21, after receiving reports of a fire.

Outside the mansion, Keith’s body was found on the front lawn, with a gunshot wound on his lower back and “four shots into his head.” Jennifer Caeiro, who was found inside on the stairs leading to the basement, also sustained a gunshot wound to the head as well as “multiple stab wounds to her torso.” Sophia was found on the stairs leading to the second floor, while her brother’s body was in the kitchen. Both sustained fatal stab wounds.

“This one is the most brutal cases that I've seen in my experience here,” Monmouth County Prosecutor Christopher J. Gramiccioni said in a press conference at the time.

According to the affidavit, investigators found a plastic container with bloody clothing and latex gloves, along with a large number of “legally registered weapons” stored in a safe in Paul Carneiro’s basement, including a Fiocchi 9mm.

Shell casings from the gun were “consistent” with those recovered from Keith’s home, authorities said.

A red gas can and a charred, rubber glove with blood were also found at Paul Carneiro’s home, next to the white Porsche Macan he was renting while his car was at the dealership. The car had burn marks that are consistent with gas fires, the indictment says. Inside, investigators found a backpack containing a laptop, Paul’s passport, a silencer, and a Flir night-vision scope that “attaches to a firearm,” according to the indictment.

On Nov. 21, the day after the fires, Caneiro was arrested and charged with aggravated arson for torching his own home. Eight days later, he was charged with murdering his brother and his brother’s family.

Caneiro pleaded not guilty in November, and his lawyers claim he has been “wrongly accused.”

“Paul Caneiro loved his brother, loved his sister-in-law like a sister, loved those children and would never do anything to harm them,” said defense attorney Mitchell Ansell. “There’s no reason on this earth for him to have harmed them.”

Caneiro is currently at the Monmouth County Correctional Institution pending his trial.