Why was he free?

It’s almost unfathomable to think that Philadelphia has lost still another police officer in the line of duty. Sgt. Timothy Simpson became the became the fourth cop to die in the line of duty in less than seven months when his cruiser was rammed by another car Monday night.

But what is even more galling about this case is what we are learning about the person who was driving that other car.

William Allen Foster, 41, of Levittown, is being described as a career criminal. Police say he came into the city to buy drugs and was fleeing police when his car slammed into Foster’s police car in the city’s Port Richmond section.

After his arrest, Foster apparently bragged to police that he often eluded arrest.

He’s had enough practice at it. Foster has a lengthy arrest record. And one thing stands out: Why exactly was this guy still out on the streets?

It’s a question that is often asked in such incidents. For once it would be nice to get an answer.

In the meantime, Philadelphia police again will prepare to bury one of their own. You begin to wonder just how much the department can take.

Simpson leaves behind a wife and three kids, including teenage twins.

And Foster? He’s safe and sound back behind bars. Where he likely should have been in the first place.