Pictured: Long Island son Joe DeLucia Jr who killed family then himself in shock murder suicide after his mother's funeral

A distraught son killed four of his family before turning the gun on himself as they met to discuss winding up his late mother's affairs.

Joe DeLucia Jr opened fire inside the family home on Wyoming Court in Syosset, on Long Island, just before noon on Sunday.

Neighbors heard anguished wailing, crying, and screaming before DeLucia fatally shot himself on the front lawn minutes after the massacre.

His mother, family matriarch Theresa Martha DeLucia, 95, died on August 19 and was buried on Friday, which he was still greatly distraught about.

DeLucia, who has mental health issues, is believed to have been unable to handle the prospect of moving out of the family home, where he lived all his life.

Real estate agent Mary Macaluso was asked to come to the house on Sunday to discuss selling the property, but arrived to find a crime scene.

Neighbor Randi Marquis told DailyMail.com that Theresa's will declared the house should be sold and anyone living there had to move out.

'He was afraid that he was going to be homeless... His sister told me that he stopped taking his medicine on Saturday, and once he stops taking the medicine, that's it,' she said.

'He had this planned. I don't know where he got the gun from.'

The victims were DeLucia's brother who flew in from North Carolina, a sister from Tampa, and another sister from Long Island, along with her 26-year-old daughter.

One of the sisters was said to have offered to DeLucia in at her home and look after him, and it is not clear why he turned her down.

Marquis explained that the gathering was supposed to double as a birthday party for one of DeLucia's sisters.

She was at home organizing food for the party, intending to come after Macaluso was finished discussing the house sale, when she realized something was wrong.

'When I saw the ambulance I just knew,' she said, though she initially only thought DeLucia only took his own life.

'When I went over to the neighbor and a neighbor said, "he took all of them"... It was selfish.

'I didn’t see this coming. God forbid I was going to be there. I was going to go there and sing happy birthday and I told them not to eat I was going to bring a lot of food.'

Marquis said DeLucia was born with the umbilical cord wrapped around his neck and and was deprived of oxygen during birth.

She said he was a retired paramedic who worked as a mechanic in Hicksville and drove himself to work, then home right away to look after his mother. 

'He loved his mom. He was always there. He was there every day in the hospital,' she said.

Marquis said DeLucia's sister, with whom she was close friends, told her she was worried about her brother in the days after their mother's death.  

The neighbor spoke with DeLucia, who was talking about ending his life.

'I told him in the Catholic religion you don’t do that... now is not your time. All your sisters and brothers are here,' she said.

Marquis said Theresa had a bad fall in April and her daughter said her health began to decline after she stopped going to physical therapy.

'I was close with Terry, I took care of her sometimes, visited her, cooked for her, her children used to play in my backyard,' she said through tears.

'I was also very close with one of the daughters and I met all of her siblings again [at the funeral] on Friday.'

Marquis said the 26-year-old woman was Theresa's oldest grandchild, who had just finished university and was figuring her life out.

'She was also like a daughter to me, since I have four boys but never a daughter,' she said.

Police said they responded to a call about shots fired in the quiet cul-de-sac where they found a man suffering from a self-inflicted gunshot wound on the front lawn just before noon on Sunday.

'The mom just died, and they were selling the house,' real estate agent Mary Macaluso told Newsday.

She noted she was supposed to be meeting relatives at the home at around noon - but by the time she arrived, authorities had already closed the street. 

'The kids were all here for the funeral, and they asked me to come look at the house,' Macaluso said, explaining that one of DeLucia's children asked her to meet with the family so they would know what to do before listing the home, which is estimated to be worth nearly $900,000 on Zillow. 

The family wanted the assessment done quickly because two of the family members came up from Florida for the funeral, and were headed back soon, she noted.

But the suspect, believed to be in his 60s, had lived in the house his entire life, and neighbors say losing the home was just too unbearable for him.

'I didn't think that he'd take his whole family, his siblings,' one neighbor told Fox 5 New York.

'I thought maybe he was distraught and he did this to himself only.'.

Other neighbors noted that they heard gunfire, as they remained shaken up by the grisly scene.

'At first I heard it was a murder-suicide, and that's pretty bad,' Mike Steffens told ABC 7. 'And then I heard four people murdered and then a suicide, so it was something you don't hear very often, let alone in your own town.'

Another resident, Wendy Paisner, called the murder-suicide a 'tragedy for the family' in her remarks to NBC 4 New York. 

Nassau County police say they are not identifying any of the victims, the shooter, a possible motive or whose gun was used in the shooting.

They will release more information about their findings on Monday.