Scapegoating a single cop would compound the tragic murder of Amy Lord. Police officers are not infallible. Still it is critical that the Boston Police Department determine precisely why charges were never filed against Edwin Alemany in the assault of a Mission Hill woman last year when she was discovered unconscious, with his wallet and ID in her hand — and most importantly they must share the results of that investigation with the public.

Given what we now know about Alemany’s criminal record — 34 charges as an adult, 10 felony convictions, and 18 arraignments as a juvenile — an arrest in last year’s assault might have kept him off the street. And yes, that leads us all to wonder whether it might have prevented Lord’s death.

We say “might have,” not just because as of this writing Alemany officially remains just a “person of interest” in Lord’s killing but because candidly we question whether the outcome would have been any different from the dozens of previous arrests. There should be a full review of the court proceedings that left Alemany free to roam the streets.

But as Commissioner Ed Davis said, the BPD’s standard for an arrest is not absolute proof of guilt but probable cause, which the police clearly had. An internal complaint accuses the detective of “failure to properly conduct an investigation and move a case forward for potential prosecution.” He will be stripped of his detective rating. All of that is warranted. But his immediate superiors need to answer questions, too, and face sanction if their actions contributed to the decision not to move forward.

Davis has also launched a review into all unsolved assault cases to determine whether there are similar loose ends that investigators might have missed. He should also consider revised training procedures.

We were particularly troubled by the comments from the victim in last year’s assault that officials barely followed up on the 2:30 a.m. beating that left her unconscious, after she was told Alemany wouldn’t be charged.

An ex post facto review of police and court proceedings will bring little solace to Lord’s grieving family and friends, nor is it likely to soothe nerves in South Boston and every other neighborhood in this city where women fear becoming victims.

But if we don’t learn from such serious mistakes, that fear will be entirely justified.