Capt. James Clark, Homicide Unit commander, said the second man sought is Chancier McFarland, 19, of the 1400 block of North 23rd Street in North Philadelphia.
He said McFarland should be considered armed and dangerous and asked anyone with information about his whereabouts to contact police.
"Turn yourself in," Police Commissioner Charles H. Ramsey said at a news conference.
As for Jones, Ramsey called him a "violent thug."
"Thank God we have him," the commissioner said, adding he hopes Jones "spends the rest of his miserable life" in prison.
On Thursday, Jones' 19-year-old brother was taken to Police Headquarters for questioning after showing up at the North Philadelphia's 22d District in the company of State Rep. W. Curtis Thomas, D-Phila.
Ramsey told reporters at Police Headquarters earlier today that the brother was not a suspect and investigators only wanted to question him.
Walker, a 19-year veteran of the force, had just finished his night shift at the 22d District shortly before 6 a.m. Saturday and was walking to a bus stop when he was killed in the 2000 block of Cecil B. Moore Avenue.
Surveillance video released this week showed two men walking nearby, then apparently spotting Walker. Other footage captured Walker glancing over his shoulder toward the men, who followed and caught up to him.
They stopped him and announced a robbery, police said, and as Walker tried to draw his off-duty gun, he was shot in the chest, the stomach, and one arm.
He died at Hahnemann University Hospital.
Ramsey said he has spoken to Walker's relatives and the news of Jones' arrest gave them "some measure of relief."
There is no word yet whether anyone will be able to claim all or part of the $118,000 reward posted in the case.