When they opened the door of their Hallandale Beach condo to take the dogs out for a walk Monday night, Danielle Melendez and Peter Paulgar found their neighbor laying on hallway floor.

“She was like a fish out of water, gasping for air,” said Melendez.

At that point, neither Paulgar or Melendez knew their neighbor had been shot.

“At first we didn’t see a lot of blood,” Melendez said.

As paramedics vainly tried to save the 47-year-old woman’s life, police knocked on the door of the woman’s unit at Park Layne Towers, 400 Golden Isles Dr.

“Go away,’’ a man’s voice replied, according to Hallandale Beach Police Chief Dwayne Flournoy.

It was the beginning of a nearly five-hour stand-off between a SWAT team and the dead woman’s 57-year-old husband.

At about 2 a.m., police tossed a chemical canister into the apartment. Shots rang out, and when the officers entered, they found the man inside dead from a self-inflicted gunshot wound.

The dead couple have not been identified pending notification of next of kin.

Neighbors say the scene cause a commotion on the normally quiet street lined with condominiums.

A two-block stretch was closed most of the night, preventing many residents from getting into their homes.

Betty Simon, who lives in the apartment building across the street, said she heard what sounded like fireworks, and then watched the scene from her balcony.

“There were so many police cars,” she said. “I knew something very serious happened.”

Tina Polek, who lives in the same building, said the couple recently came over for dinner. They ate Italian food and chatted for hours.

“He was a jokester,” said Polek, adding that man was “handy,” and laid tile on her terrace. “They were a beautiful couple. I just don’t understand what happened.”

Police found a letter inside but have not released the contents of the letter or who wrote it.