(CNN) -- Philadelphia city officials said Wednesday the beatings of three suspects, captured on video by a television news crew, were "unacceptable," and added officers' emotions are running high after the slaying of a sergeant last week.
Aerial footage from WTXF shows police officers beating suspects in Philadelphia, Pennsylvania.
"We certainly are concerned about what we saw on the tape," Police Commissioner Charles Ramsey told reporters Wednesday afternoon. "The matter is being taken very seriously, even though emotions run very high in our department right now, because we just had our third officer killed in the last two years ... obviously, that puts a lot of stress and pressure on the officers.
"But having said that, we do expect them to maintain a standard of conduct on the street that is above reproach," he said.
Ramsey earlier said an internal investigation was underway into the incident caught on video Monday by WXTF-TV. He said police officers saw the suspects fire shots, injuring three people standing on a street corner before fleeing in a vehicle.
The video shows at least a dozen police officers pulling the suspects out of a car after a vehicle chase Monday night.
At least eight officers are seen either kicking, punching or striking the suspects with batons while the men lie restrained on the ground.
Two men are struck at least 20 times each. Watch footage of the incident »
Ramsey said a sergeant and five officers have been removed from street duty in connection with the incident so far. He said he has been in contact with the district attorney's office, which will receive a copy of the tape and decide whether to file criminal charges.
Authorities are still in the process of identifying the officers on the tape, he said, and have sent the video to be enhanced. "We're going to continue our investigation," he said.
"We'll identify everybody who was there at the scene to the best of our ability. All six were there. The extent of their involvement, I don't personally know. The sergeant should have taken some kind of supervisory action to intervene," Ramsey said.
A fourth suspect in the shooting escaped on foot, he said.
Lemoia Dyches, the mother of one of the suspects, says she's been unable to see her son, Lionel Dwayne Dyches, 24, since his arrest.
"They wouldn't even permit his attorney to see him," she said. "They're hiding him. It strikes me as strange."
However, police made mug shots of the three available to reporters later Wednesday. In the photos, at least two of the suspects have visible cuts and bruises.
"It is not acceptable, of course, to do anything less than the professional standards we expect from our police officers," Mayor Michael Nutter said. "The behavior that was at least exhibited on the tape is unacceptable."
On Saturday, police Sgt. Stephen Liczbinski was shot and killed with an assault rifle while attempting to apprehend bank robbery suspects. One suspect was killed by officers in the confrontation and another has been arrested. The third suspect remains at large.
Stress levels among officers on the street are "simply too high," and the department aims to eliminate 12-hour shifts, Ramsey said earlier Wednesday.
"This is massive because of the number of officers we've had killed in a short period of time ... we want to make sure officers are psychologically prepared to deal with everything," he told reporters.
After seeing the videotape, the mother of one of the men arrested said, "I just burst out and cried. I was appalled by it."
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