A horrifying murder-suicide on New York's Long Island left five people dead, and it reportedly happened before a family was set to meet with a realtor to sell a recently deceased woman's home.

Nassau County police arrived at the home on Wyoming Court in Syosset around noon Sunday – about 30 miles east of New York City.

Responding officers found the gunman outside, dead of a self-inflicted gunshot wound, according to authorities. They found four more victims dead inside the home.

Police did not immediately identify the victims.

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Mary Macaluso, a local realtor, told the local newspaper Newsday that she was supposed to meet a group of relatives at the address to discuss selling the home after the death of its owner and the family matriarch.

"The kids were all here for the funeral, and they asked me to come to look at the house," she told the paper. One of the siblings had reportedly asked for the meeting while other relatives were in town from Florida for the funeral.

Fox News Digital could not immediately reach Macaluso for comment Sunday.

Records and an online obituary show Theresa Martha DeLucia, 95, is the home's most recent resident and was buried last week, Newsday reported.

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The online obituary was no longer visible online as of Sunday evening.

A couple living in the neighborhood told FOX 5 New York the alleged gunman was in his 60s and had recently lost his mother, who was in her 90s. 

The couple said the son and mother had been living in the neighborhood for years. 

"I didn’t think that… he’d take his whole family, his siblings. I thought maybe he was distraught, and he did this to himself only," the neighbor told the local station.

"This is really heartbreaking. This is such a quiet little neighborhood they used to call it a bedroom community. It’s shocking," another neighbor told FOX 5.

The home had not yet been listed for sale – but real estate website Zillow estimated its value at nearly $900,000.

Other homes nearby have sold for close to $1 million, according to the site.

At least three people were stabbed during the opening day of the Notting Hill Carnival in London on Sunday, with one still listed in life-threatening condition, according to the city’s police.

The London Metropolitan Police Service said on X it was aware of three stabbings, one of which involved a 32-year-old woman who was hospitalized with life-threatening injuries.

Also stabbed was a 29-year-old man and a 24-year-old man, the former of whom was listed in non-life-threatening condition. Police were waiting on the condition of the 24-year-old at the time of the post.

"Hundreds of thousands of people came to Notting Hill Carnival today to enjoy a fantastic celebration. Our officers have been on duty working to keep them safe as part of a very carefully planned policing operation," the police service said. "Regrettably, a minority came to commit crime and engage in violence."

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Police said 15 officers were assaulted when things turned violent, though none of the officers sustained serious injuries.

Police made 90 arrests for various offenses.

Ten people were arrested for assaulting emergency workers, 18 for possession of an offensive weapon, four for sexual offenses, one for theft, four for robbery, six for assault, one for public order offense, eight for possession of drugs with distribution intent, and 30 for possession of drugs – four arrests of which were for possession of nitrous oxide.

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Ahead of the carnival, police announced they had been authorized to order the removal of face coverings being used to conceal a person’s identity. Anyone refusing the order, police said, could be arrested.

The Notting Hill Carnival attracts hundreds of thousands of revelers each year, who pack the streets of west London for two days, during one of the world’s biggest celebrations of Caribbean music and culture.

This year, the festivities take place Aug. 25-26.

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The carnival traces its history back to 1958, when Trinidadian human rights activist Claudia Jones began organizing a gathering to unify the community after a series of racist attacks on Black people in the Notting Hill neighborhood.

Launched in 1964 with a few Trinidadian steel bands, it has grown into a huge annual street party involving colorful floats, thousands of calypso dancers in spectacular feathered costumes, almost 20 steel bands and more than two dozen sound systems.

The carnival returned to the neighborhood’s narrow streets in 2022 after two years when it had to be held online because of the coronavirus pandemic.

The Associated Press contributed to this report.