Who shot Niko?

The shooting of Niko E. Nunez on a steamy summer night in 2014 was a prosecutor’s nightmare.

The killers pulled up in a Ford SUV and sprayed bullets at Nunez as he walked down Aguadilla Street in the South End. Outdoor shootings leave less evidence.

And it was the middle of the night — around 2:45 a.m.

And as in many cities, police and prosecutors in Boston sometimes face scared or reluctant witnesses in gang crimes. In initial statements after the shooting, police said they were looking into the possibility the shooting was gang related.

Nunez, a 20-year-old father of a 7-month-old son, had no gang connections, friends told Globe reporters at the time. He had just left a block party in Villa Victoria the night of the shooting. If authorities know the motive for the murder, they’re not saying.

Jake Wark, a spokesman for Suffolk District Attorney Dan Conley, said that the investigation remains open and that the killing “could be one witness away from being solved.”

“If someone out there has information that they were afraid or unwilling to share two years ago, we want to reiterate that they can do so safely and even anonymously if they wish,” he said. The phone number is 617-343-4470.

If the crime highlights the importance of witnesses, a separate incident a few months later points to the chilling extent to which acts of violence in the city are often linked by only a few degrees of separation.

Less than a year later, a close friend of Nunez, the Rev. Shaun Harrison, would be arrested in another high-profile case and accused of shooting a 17-year-old, who survived.

Harrison is scheduled for trial Oct. 17.

Justice for Nunez, meanwhile, is still elusive.