New photos show the grisly scene inside a Long Island house of horrors where a murder-suicide left five members of the same family dead — as a neighbor said one of the victims was celebrating her birthday the day she was killed.

The images, taken Tuesday morning, captured the back den where cops say madman Joseph DeLucia killed his three siblings and a niece with a shotgun in a fit of rage over their plans to sell his late mom’s home on Wyoming Court in Syosset.

The wood-paneled room is filled with old-fashioned furniture and items, such as wooden captain’s chairs, piles of newspapers and magazines, a wooden table covered by a vinyl tablecloth, crocheted throw blankets and a well-worn couch.

A cup of iced coffee still sat on a living room end table — police said the family had stopped at Starbucks to get drinks before meeting with a local realtor to discuss selling 95-year-old matriarch Theresa DeLucia’s tiny North Shore house.

The only sign of the tragedy was a pair of bloodstained white sheets that lay crumpled near each other on the floor, just below the table.

It’s not clear how they got there, or whether they were being used to clean up the blood that streamed from DeLucia’s four victims before he ran outside and turned the shotgun on himself, with cops finding him dead on the lawn just before noon Sunday.

A balloon could be seen floating in the corner of the room — and a neighbor, who gave her name as Randi, said the family intended to celebrate victim Tina Hammond’s birthday on Sunday.

The neighbor said she was very good friends with the 64-year-old Tina, who showed up at her mom’s house with her daughter, 30-year-old Victoria Hammond.

“I got to know her because I helped her mom, she was elderly and couldn’t take care of herself, we became best friends,” Randi said, describing Tina, who lived with her daughter in East Patchogue, as “a good person and always upbeat.”

The neighbor was headed over to the house to celebrate, too, but something told her to wait just a little bit — so she went to get food for the party instead.

The decision may have saved her life.

“I went to pick up the food first, and came back and saw the police here. If I didn’t pick up the food, I would have been in the house. And possibly be dead also,” the shocked woman said. “There is a God.”

The gathering turned into a dizzying bloodbath around noon Sunday when DeLucia, a 59-year-old mechanic, gunned down his niece Victoria and her mom, as well as two other siblings — Joanne Kearns, 69, of Tampa, Florida, and Frank DeLucia, 63, of Durham, North Carolina.

Authorities have said DeLucia, a former EMT, had a history of mental illness and could not comprehend that he’d have to leave the home he’d lived in his entire life because his siblings were going to sell it following their mom’s Aug. 19 death.

On Tuesday, Tina Hammond’s boss said she was simply an “exceptional kind of person.”

“She had a bubbly personality and was kind and friendly to everyone,” said Steve Huey, the 64-year-old manager of Giunta’s Meat Farms Supermarket in Bohemia. “Everyone here is still in shock. The whole situation, it’s surreal.”

Huey said her mom had recently become very sick, and the East Patchogue woman often had to interrupt her work shifts with phone calls to doctors or nurses.

She’d begun working as a cashier about a year and a half ago, he said. And he was immediately impressed with her work ethic.

“She was second to none,” he said. “She showed up early and went out of her way to help people.”

“She always had a smile, she always had something good to say,” he continued. “She never complained about anything — and when you’re dealing with the public for a living, that’s a miracle! It’s very, very rare! That right there tells you what kind of person she was.”

He also said she loved her daughter, Victoria, with whom she lived. Victoria would visit the store often, he said with a smile.

“They were two peas in a pod, inseparable,” Huey said. “They were always together, and they were just always really nice people.

“She was a good all-around person who is taken away too soon,” the manager added.

“You’d never think this would happen. It’s surreal. How can it be true? Everybody here is in shock. There isn’t any getting over this.”