Wilfred Labossiere, 31, of 306 Beach 19th St., was charged with second-degree murder and first-degree assault and criminal possession of a weapon, Nassau police said.
Labossiere shot and killed Christopher Mullings, 29, of Roosevelt, police said, and critically wounded the 51-year-old grandmother of Labossiere's 3-year-old son.
The woman's name was not released by police.
Labossiere had dropped off his son at the grandmother's home on Oakley Avenue early in the morning, and returned after a telephone argument about visitation, police said.
The argument continued outside the home, with Labossiere, the grandmother, and Mullings, a family relative.
A 19-year-old neighbor, who asked that his name not be published, said he had been asleep when he was awakened by a loud argument outside. He was awakened again sometime later by the sound of gunshots.
"I knew they were gunshots," he said. "They came real fast. I sprung out of bed."
The argument between Labossiere and Mullings became physical, police said. Labossiere pulled out a gun and fired multiple shots, striking Mullings and the grandmother, police said.
From his upstairs bedroom window, the neighbor said, he saw the wounded man on the front lawn and the woman on the nearby sidewalk.
"I heard her say 'Help, I'm shot,' or something like that," the neighbor said.
Police said Labossiere helped the woman into the car and her to a hospital. After entering the hospital's ambulance bay, Labossiere gave the wounded woman to hospital personnel and fled.
Fourth Precinct officers saw his car in Far Rockaway, and he was arrested without incident, police said.
The woman was reported early this morning in critical but stable condition, police said.
Labossiere was to be arraigned Tuesday in First District Court, Hempstead.
With Gary Dymski