Police Commissioner Richard Ross said Monday that he had "some concerns" about a fatal shooting earlier in the day by an off-duty officer, of a man who allegedly had driven his car into a pedestrian in South Philadelphia and then fought with the officer afterward.

"In particular, whether all the shots were necessary," Ross said at a late-afternoon news conference at Police Headquarters.

The 31-year-old suspect "probably did attempt to, at minimum, disarm the officer, which is why I was not suggesting that there was not a need for any rounds to be fired," Ross said of the confrontation, recorded on surveillance video cameras.

"At this time, we have no reason to believe this male was armed," Ross said.

The suspect, whose identity was not released, was taken to Penn Presbyterian Medical Center, where he was pronounced dead around 10:15 a.m.

Around 7:30 a.m., the suspect was driving a black Honda Civic south on Broad Street when he made a left turn onto Bigler Street and struck a man leaving a parked car, Ross said.

The suspect continued driving east on Bigler, but then made a U-turn and drove back to the intersection, Ross said.

There, "a good Samaritan used his truck to block his path," Ross said. The driver of the truck got out and apparently tried to tell the suspect that he had hit someone. The suspect allegedly got out of the Honda and began to chase the good Samaritan.

As the suspect began to walk back to the Honda, the off-duty officer, who had witnessed most of what happened, exited his own vehicle and confronted the suspect.

Witnesses said the officer identified himself as police and ordered the suspect to the ground, Ross said.

The suspect "charged the detective immediately upon the detective approaching him. There is a violent struggle that you can see where they're spinning each other around and around," Ross said. The suspect allegedly struck the officer several times.

Ross said the officer shot the suspect "several times," but declined to be more specific.

Police earlier said the officer fired at least 10 shots and that the suspect was hit in the face.

The Honda had Maryland plates and Ross said the suspect was from that state.

"We have no idea why he was here," Ross said.

Investigators were awaiting toxicology results or other evidence to explain the suspect's "erratic and bizarre behavior," Ross said.

The 40-year-old man who was hit while exiting the parked car was treated at Penn Presbyterian for minor injuries.

The officer, who earlier had been identified as assigned to the Major Crimes Unit, also was treated and released from the hospital for injuries to his head and left shoulder. He will be assigned to administrative duties while the shooting is investigated by Internal Affairs.

Ross said police had received initial reports that the suspect had tried to run down other pedestrians, but no evidence of that was found.

Ross said investigators will continue looking for more video and witnesses. Anyone with information can contact the Internal Affairs officer-involved shooting team at 215-683-1866.