Paul Caneiro, 52, was previously arrested on arson charges in the case.
In a press conference Thursday morning, Monmouth County prosecutor Christopher J. Grammiccioni told reporters that the defendant committed the murders, started a fire in the basement of Keith's Colts Neck mansion, then returned to his own home in Ocean Township to start a fire as a trick to cover up the crime.
Jennifer Caneiro was shot and stabbed, and the two children, 11-year-old Jesse and 8-year-old Sophia, were stabbed repeatedly, the prosecutor said, disclosing for the first time how the three died. However, records do say the murders took place in Colts Neck on November 20.
Prosecutors say financial motives led a technology executive in the U.S. state of New Jersey to kill his brother, the brother's wife and their young children before setting fire to their two homes. No one was injured in that blaze, which broke out hours before the one in Colts Neck.
Paul Caneiro, a 51-year-old from Ocean Township, New Jersey, has been charged with four counts of murder, one count of firearm possession, one count of knife possession, and one count of aggravated arson after he allegedly killed his 50-year-old brother Keith Caneiro, his wife Jennifer Caneiro, and their two young children.
Caneiro's wife and two daughters were home when he is accused of using gasoline to ignite their Ocean Township home, which is about 10 miles from his brother's home in Colts Neck. Their bodies were left to burn, police said.
An investigation into those businesses - and the financial dealings of the Caneiros - has been launched, the prosecutor said.More news: So Sad: Oprah Winfrey Suffered A Heartbreaking Loss On Thanksgiving Day
Honecker has not commented on the reports on the new charges.
"The fire at his home served two purposes", Gramiccioni said.
Attorney Robert A. Honecker had previously maintained his client was innocent and said Caneiro was "devastated by the news of his brother and his family's deaths". "He fully expects to be vindicated when this case finally resolves".
They both owned Square One, a technology company, and EcoStar Pest Management, both in Asbury Park.
Paul Caneiro was charged last week with aggravated arson stemming from the fire at his house.
He remains in jail without bail and is scheduled to appear in Monmouth County Superior Court in Freehold, New Jersey, on Friday.
The brothers were best friends who talked nearly daily, Honecker told CNN, adding he had no reason to believe there was animosity between them.