A man who believed he was being cut out of his mother’s will and did not want to move out of her home, has shot dead four members of his own family before taking his own life, police in the US have said.

Joseph DeLucia Jr killed his three siblings, Joanne Kearns, Frank DeLucia and Tina Hammond as well as Ms Hammond’s daughter, Victoria Hammond, at a family meeting at his mother’s home in Long Island on Sunday.

DeLucia Jr, 59, met the others at the property in Syosset, about 15 miles (24km) east of New York City, Nassau County Police Captain Stephen Fitzpatrick said on Monday.

It was just three days after Theresa DeLucia, who died last week at age 95, had been buried, he said.

But instead of discussing the planned sale of the home, where DeLucia Jr had lived his whole life, the car mechanic fired 12 rounds from a shotgun, killing the others.

He then walked out to the front garden “shouting indiscriminately” about what he had just done before turning the gun on himself, Captain Fitzpatrick said, adding that DeLucia thought “he was being cut out of the will and that he would be displaced with nowhere to go.

“Because of that perception, he decided that day to get a loaded Mossberg shotgun, 12 gauge, approach them in the rear area of the house and from the kitchen, fired 12 shots, striking all four of them multiple times. The entire family is now gone.”

His two sisters and brother were all in their 60s, while his niece was 30, police said. All four were found in the house, while DeLucia Jr was found outside, News12 said. All five were pronounced dead at the scene.

The family members had tried to convince DeLucia Jr that he would be provided for following his mother’s death, but that he would have to move out of her home.

A neighbour who identified as Randy said while DeLucia Jr appeared “sad and confused” in recent days, there were no obvious warning signs he would turn violent and said she was not aware he owned a gun.

She said: “We had no idea this was coming. If we knew he was going to do this, we would have said something, of course we would.”

The family had gathered at the house ahead of a meeting with a local real estate agent and were also celebrating Tina Hammond’s birthday, she said.

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Police said they could have used so-called “red flag” laws to stop DeLucia Jr from getting hold of a firearm if they had known he was dealing with mental health issues.

Nassau County Police Commissioner Patrick Ryder said officers only learned after the shooting that neighbours were concerned he might harm himself or others as he had been emotional and distraught following his mother’s death.

Captain Fitzpatrick said: “We’re not saying this incident could’ve been averted, but maybe it could’ve.”

Detectives were still looking into reports DeLucia Jr dealt with mental health issues, adding that he was a hoarder and the house was packed with tools and other car repair items, he said.

The only time police had been called to the residence in recent years was for a wellness check, and his only arrest was for driving under the influence back in 1983, he said.