Detective Brian Stevenson, an 18-year veteran with the department, would have turned 38 on Sunday, police spokesman Anthony Guglielmi (goo-lee-EHL'-mee) said. Stevenson was out celebrating with a friend after 10 p.m. in the southeastern part of the city when it happened.
"The preliminary investigation revealed an altercation took place over a parking place," Guglielmi said. As the dispute escalated, he said, "A suspect pulled a rock or large piece of concrete from the ground and struck the officer with it."
Stevenson sustained head trauma and died later that night at Johns Hopkins Bayview Medical Center.
The suspects were described only as a man and a woman.
"Once they struck the officer they fled," the spokesman said.
Guglielmi said witnesses led investigators to "people of interest" who were taken into custody.
"They are being interrogated right now by homicide detectives," he said early Sunday. "We are optimistic that an arrest is going to be forthcoming."
He declined to say how many were taken into custody.
The attack happened in what Guglielmi described as "a very safe part of town." He said he lacked the words "to describe how heinous this act of violence is for something as truly petty as a parking space."
Stevenson, who was married and had children, was assigned to a detective unit that investigates crimes such as shootings, assaults and robberies, Guglielmi said.