Police were still investigating and had blocked off the street as onlookers in the working-class neighborhood clustered nearby.
Samuel joined the New York Police Department in 2000 and was most recently assigned to a precinct in Queens.
A next-door neighbor who identified herself as an aunt said she could find no reason for the deaths. Agnes Samuel, 83, said the officer was always smiling and waving to her, and seemed like a happy person.
"It's terrible," Agnes Samuel said as she choked up. "For people to take a life like that. Oh, Lord!"
Around the corner from the crime scene, 19-year-old Stephen Elias, a friend of Dondre's, said he was relieved the teenager had escaped.
He said the family had lived in the neighborhood at least a decade. Dondre skateboarded and played soccer with kids in the neighborhood, and "kept himself out of trouble," Elias said, but his mother didn't like some of his friends.
"She looked very angry a lot of the time — just angry," said Elias, clenching his jaw and staring ahead to demonstrate "how she was most of the time." He added, "I don't know what made her so mad."
Associated Press writer Verena Dobnik contributed to this report.