Then there was the next set of pictures – the crushing moment three teenagers were convicted of Harper’s manslaughter but not murder – and the despicable shots as the killers and their families cheered at the verdict, gave thumbs up, looked, as Lissie’s mum put it, “like they’d just been at a football match.” There is something deeply repellent about crimes committed without remorse.

Yet if all of that still felt as upsetting as it did when first reported in 2020, this documentary, sensibly, chose not to dwell on the killing itself. Instead the focus was on Lissie Harper, Andrew’s widow, and how she has battled – an overused word but overwhelmingly the right one in this case – to change the law for those convicted of killing an emergency worker while they were committing a crime, so that it carries an automatic life sentence. The current state of play was made clear with the stinging note that, when released, all three killers will be no older than Andrew Harper was when he died.

As a documentary, The Killing of PC Harper existed in uncomfortable territory: step back from the case itself and you were watching a widow trying to find meaning, a reason to go on, amid a pointless crime and inconsolable grief. It’s a lonely walk and, at times, the viewer couldn’t help but feel like we were intruding.

And truth be told, Sir Trevor McDonald in full nodding sonorousness won’t have been to everyone’s taste. But Lissie Harper, it became clear, wanted this kind of documentary made, wanted headlines and attention, because without them nothing would have changed. Harper’s Law is expected to go on the statute book in the next few months. If the prospect of a film like this one has done anything to expedite that painful process, then it was worth the effort.