Do you know what this police show or film was?

In 2000 or 2001, when I lived in England and I was 4–5 (4 in 2000, 5 in 2001), I saw this show or film on the television – I assumed it was a show. My parents or at least my mother were watching it, and I was there at the time.

All that I remember was that there was an African-American cop (I could tell by his American accent), who, as the camera gave a close-up shot of his face in an alley by a street with a black car in the background (either still or moving), told the main character (there were several main characters in the story, sorry for forgetting that) that he had shot a 14-year-old boy when he was a young cop after he mistook his finger gesture gun with a real gun, as he made a finger gesture and was smiling – not out of sadism you know, but rather for the same reason that the teenage girl in the film “Gremlins” smiles when she talks about the death of her father, if you know what I mean.

By the way, as for my last question, I found out shortly after receiving the answer that it might be “Diagnosis: Murder” that it was – being a little kid, I could not distinguish accents, and I assumed that all television shows were set in England! Seeing the episode jogged my memory, and I could remember things that I couldn’t remember before, like Dick van Dyke’s character and his associate examining the metal holes where the metal spikes went into after the murder (my memory of his character saying that the magician was dead was garbled for want of a better word, as I believe “garbled” only refers to words). Anyways, thank you, whoever suggested the idea (sorry, I forgot your name, and I apologize)!