A US man killed his three siblings and his niece in a murder-suicide in New York on Sunday, as the family came together at the shooter’s home to discuss the will of their recently deceased mother and grandmother. Joseph DeLucia Jr., 64, fatally shot all four relatives outside the back of the home before heading out to a seat in the front yard where he turned the gun on himself.

Police said he may have “panicked” over the family’s plan to sell the Long Island home, in Syosset, where he had lived his entire life, Det. Capt. Stephen Fitzpatrick said on Monday.

Know the news with the 7NEWS app: Download today DeLucia Jr. fired 12 times to kill his four family members before shooting himself in the chest. The victims were identified as 69-year-old Florida woman Joanne Kearns, 64-year-old North Carolina man Frank DeLucia, 64-year-old New York woman Tina Hammond and her daughter, 30-year-old New York woman Victoria Hammond.

The scene at the family home on Wyoming Crt was one of the most “horrific” scenes ever witnessed by Nassau County Police Commissioner Patrick Ryder, he said. Ryder spent a press briefing Monday pleading with the public to come forward when concerned about someone’s mental wellbeing. Neighbours, he explained, shared accounts after Sunday’s murder-suicide of the man allegedly warning of a shooting.

The commissioner said DeLucia Jr. had told neighbours, “If you hear gunshots, don’t bother calling 911 it’ll be too late.” Ryder stressed that po.