He apparently was able to get his gun out of his holster before he died; the gun was found under his body. It could not immediately be learned whether he had fired any shots.
"I can honestly say his life was more dedicated to the church than work," said Roosevelt Poplar, vice president and chief of staff of the Fraternal Order of Police Lodge 5. Poplar said he had known Walker ever since the officer joined the force nearly 20 years ago.
"You won't find two people to say anything bad about him," Poplar said.
Walker was found facedown in the 2000 block of Cecil B. Moore Avenue near Woodstock Street early Saturday. He was in street clothes and police believe he was walking to a bus stop.
It appears robbery may have been a motive.
Walker was pronounced dead at 6:23 a.m. at Hahnemann University Hospital.
No arrests had been made by Saturday night.
Walker was not married and had no children. He is survived by his mother and five siblings. He was up for retirement this year.
The funeral will be handled by the Cordoza Jacks Funeral Home in Northern Liberties, but arrangements had not been completed.
In a statement, Mayor Nutter said: "For the third time this year, Philadelphians and members of the Philadelphia Police Department have been visited by tragedy with the violent death of a respected, veteran police officer."
He referred to the deaths of Officer Brian Lorenzo, who was killed while driving home from work July 8 by an alleged drunken driver, and of Officer Marc Brady, who was fatally injured when he was struck by a car July 15 while riding his bicycle.
Also, Officer Milan Merke died in June as the result of injuries suffered when he lost control of his motorcycle.
Nutter called Walker "a committed public servant, beloved by his family, friends, and colleagues. Our condolences and prayers go out to all of them as they cope with their grief in the loss of this good man."
Nutter's office announced he had ordered all city flags lowered to half-staff in Walker's honor. The mayor also asked residents to offer police officers their condolences and help with the investigation.
"The department's in mourning," Police Commissioner Charles H. Ramsey told reporters outside Hahnemann. "This has been a terrible year."
In addition to Walker's slaying, Nutter addressed the deaths of three others who died late Friday and early Saturday as a result of gun violence.
In all, the slayings brought Philadelphia's homicide toll to 227 for the year. Homicides are up about 12 percent over last summer.
"We offer our condolences and prayers to the families of these men," Nutter said in a statement. "We will not make headway in dramatically reducing the scourge of gun violence and the proliferation of illegal guns until we as a community stand together and offer all information that we have on the perpetrators of violence in our city.
Ramsey comforted Walker's relatives as they arrived at Hahnemann on Saturday morning. As one car dropped women off at the emergency department door, anguished cries could be heard and one woman dropped to the ground.
Ramsey called Walker a "mellow" man who was always smiling.
"He was known as a gentle individual," Ramsey said. "He wouldn't harm a fly."
Walker's mother was notified of the death while at work. Ramsey said she told him she'd never dreamed she'd be thinking about funeral arrangements for her son. Some relatives were notified by Walker's uncle, Stephen Cassidy, a lieutenant in the 18th District.
Early on Saturday, Walker had finished his shift and was preparing to leave for a bus stop. A coworker offered him a ride home, but Walker declined, saying: "It's a nice day. I'm going to walk."
As the officer walked west on Cecil B. Moore Avenue just before 6 a.m., he apparently encountered a man, or men, near 20th Street with a gun.
After the shooting, a man fled south through a vacant lot and a K-9 unit was called to track him but had no success.
Ramsey said the type of gun used to shoot Walker was still unknown. A backpack and wallet found at the scene were believed to have belonged to the officer.
Police believe they have a witness and are talking to others.
A devout man, Walker began attending services at Deliverance Evangelistic Church about six months ago. He was a deacon at his previous church, according to a cousin, Donna Seawright.
A graduate of Ben Franklin High School, Walker graduated from the Police Academy in 1993. He had been in what is now the 22d District since 1994.
Walker was a "turnkey" officer who monitored a holding-cell room at 17th Street and Montgomery Avenue. The turnkey officer works fingerprints, photographs, and processes prisoners after they are arrested.
"Obviously, the officers are very upset at the loss of our brother officer," Sgt. Gregory Caputo of the 22d District said.
Walker was known for taking children to thrill shows, staging little fairs for neighborhood youths, helping the homeless, Poplar said.
He was such a laid-back person that Nate Griffin, who managed the apartment building where Walker formerly lived had a difficult time imagining Walker firing a gun.
"I could see him taking too long to shoot, almost hoping that he wouldn't have to," said Griffin, of the Westfield Apartments in Wynnefield.
Walker lived alone there for about nine months and moved out in February, Griffin said. He said Walker told him he had suffered a ministroke while at Westfield, with a slight memory lapse being the only lingering effect.
From Westfield, Walker apparently moved to the Fairmount Terrace apartment complex in Wynnefield Heights.
Shortly after moving in, Walker locked himself out of his apartment, resident Paul Alston said. Alston found Walker sitting in the lobby and asked whether he needed help.
Walker asked to use Alston's cellphone to call his family. When Walker's mother and sister arrived at the complex, the officer thanked Alston.
"He asked me my name. I told him Paul," Alston said. "[Walker] smiled, saying, well, 'I'm Moses - we're the Old and New Testament.' "
Seawright said Walker never worried about being killed on the job. "He was always kind and sweet and well-mannered," she said.
At the scene early Saturday, officers and homicide detectives hunted for evidence. A car parked near where the officer's body was found was taken away. An officer said the car was not involved in the crime but was being dusted for possible prints in the event the shooter had gone near it.
"It's unbelievable. It's tough," Ramsey, who was wearing running shoes and civilian clothes, said of the loss. "We literally just removed the mourning bands from our badges last week for Officer Lorenzo."
At the 22d, an American flag was flying at half-staff for other officers who had lost their lives.
Police asked businesses in the area for any surveillance footage that might help.
A $20,000 reward has already been posted for information in Walker's killing. The Fraternal Order of Police offered an additional $10,000.
Police ask anyone with information to call 215-686-3334 or 3335.
"Somebody knows who did it. Somebody knows what happened," Ramsey said. "They need to come forward."
Contact Frank Kummer
at 215-854-2329 or firstname.lastname@example.org.
Staff writers Harold Brubaker, Jonathan Lai, Mike Newall, and Morgan Zalot contributed to this article.