That video was released in a news conference on Monday morning. Authorities have also announced that the reward has been increased to $88,000.
RELATED: Also watch the video on the PhillyPolice.com YouTube channel
Officer Moses Walker Jr., 40, was slain during a stickup by two men as he walked from his north Philadelphia police precinct to a bus stop at around 6 a.m. Saturday. He had just finished his shift and wasn't in uniform, clad instead in shorts and a baseball cap and a large backpack on his shoulders.
"He looked like a young civilian walking down the street, and we think that's why he was targeted," said Capt. James Clark, head of the homicide unit.
The four-minute video shows Walker looking over his shoulder several times as he walks along a streetlight-illuminated sidewalk, followed by grainy footage of two men walking behind him, first on the opposite side of the street and then crossing over. Out of the camera's view further down the block, the 19-year police department veteran was shot.
"I realize we don't have a real clear view of the suspects, but someone may know who they are just by clothing, the way they walk, the fact that they may hang around at that time of morning in that area," police Commissioner Charles Ramsey said. "Let us decide if any information you have is relevant. Do not decide that for yourself."
A third man in the video, who police believe had no involvement in the crime, was a witness to the shooting and gave police some details about what happened.
"Two males approached (Walker), one of which had a gun, a robbery was announced and he demanded money," Clark said. "During this time, the officer attempted to pull out his off-duty weapon ... one of the males fired, striking him three times: once in the chest, once in the stomach and once in the hand."
Police say the suspects likely didn't know Walker was a police officer when they approached him.
Police say Ofc. Walker pulled out his off-duty weapon at which time he was shot in the chest, stomach and hand.
Ofc. Walker, who was unmarried and had no children, was pronounced dead at a hospital in a city where on average nearly one person has been slain every day this year.
Earlier Monday, police pulled over a white Chevy in North Philadelphia and took a person into custody. That person was wanted for a similar armed robbery in the area. While police say they have not made a connection to Officer Walker's killing, they wanted to question that person.
Clark said three or four armed holdups fitting a similar pattern have occurred in the area over the last couple of months and added that the killers probably live near the scene of the crime.
"We know people out there know who they are," he said.
If you have any information about the suspect or the crime you can submit a tip by dialing 215-686-TIPS (8677), text TIP to PPD TIP (773847) or through phillypolice.com.
Officer Walker remembered at vigil
The family of Moses Walker, Jr. gathered at the North Philadelphia murder scene to remember a man who was dedicated to his family, his faith and his brother and sisters in blue.
"My son served," said the officer's mother Wayne Walker. "He served everybody. He served the city. He served his family. He served his nieces and nephews. I want to thank God for my son."
"Whatever it was about, it wasn't worth taking his life. You took him away from his family. You took him away from the people who loved him and the people he loved," said Anthony Walker.
Walker is survived by his mother and 6 siblings; a tight knit family struggling over his senseless murder.
"I love my brother, and I know my brother is up there looking down on all of us, and I know he hurt, because we are hurt," said Walker.
Funeral arrangements have not been announced.
