And Singleton's mother wants to know what took so long.
Around 9:45 p.m. on Sept. 19, 2011, Singleton was outside his girlfriend's home in Brooklyn when he was shot in the back, police said.
Singleton's mother, Monica Cassaberry, said that in the aftermath of her son's death, she went to the 81st Precinct where she saw surveillance video that was collected from a corner store and a nearby house.
"I saw a young man pacing back and forth," she told ABC News on Thursday, describing the video. "As the store started to close, the young man proceeded to go on Greene Avenue in front of the store. Then there's a private house right by the store and they had a bush, like a tree. It was still in bloom, still greenery, so that person hid by the bushes."
When "my son proceeded to get closer to the corner," Cassaberry said, "the young man came running out" from the bush.
"I guess he was running after my son ... or my son must have saw a gun in his hand," Cassaberry said.
She said then, according to the surveillance video, "my son tried to get into the street between a Jeep and a car. The young man extended his arm, he shot one time. You saw the fire come out of the gun."
"I saw my son stumble back to the front of his baby mother's house, and he dropped," she said.
After Singleton was shot, the gunman fled the scene on foot, heading westbound on Greene Avenue, police said in a statement Tuesday.
Cassaberry said the suspect she saw on surveillance video in 2011 is definitely the same man seen in the person of interest photo release by police on Tuesday. She believes the released image is from when he was pacing by the store.
"I know what I saw from the footage," Cassaberry said. "It will never leave my brain. It's etched in."
Cassaberry said she doesn't know why police aren't releasing the surveillance footage in full.
She said she initially asked detectives to release the video but she "was getting the runaround."
"I feel they should have done more back then, but I'm not gonna stop," Cassaberry said. "My son will never be back here on earth. And it's gonna always leave me empty. But I have to have some form of justice."
The NYPD did not immediately respond to ABC News' request for comment on the video.
Singleton had a 2-year-old son who saw his father's body after he fell, Cassaberry said. That boy is now an 11-year-old honors student.
"He's a sweetheart," she said. "I'm never gonna allow him to forget his father."
Anyone with information is urged to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS or at WWW.NYPDCRIMESTOPPERS.COM.