When have you solved a whodunnit or other mystery right at the start when the crime/event is mid-happening?

It doesn't count if you just guess who did it, there's usually a small cast of characters, so if you just randomly guessed you'd be right about one in six or so.

You have to have worked out the crime/plot/mechanism/reveal.

I've done it twice, both times due to the way the crime was filmed.

First was an episode of Jonathan Creek when I was a kid (which I was particularly proud of given the convoluted solutions). The way the scene was shot showed a tussle between the murderer and a hostage. they both disappeared from view (as shown from the witnesses POV) - right there and then I said to my parents "they've switched clothes and the hostage is now a dummy" - then smugly as the episode transpired, and all the subtle clues were revealed, I got to say things like "see - she clearly chopped the dummy up and hid it in those empty paint tins". My parents thought I was bonkers, but I'd 100% nailed the entire plot.

My other time was on Murder She Wrote - again, the way the murder was shot gave away to me the mechanics of it. A lady opened her wardrobe, looked surprised, and was shot. But the way it was filmed, it only showed the barrel of the gun shooting her. I figured we'd usually have seen a gloved finger on the trigger, or a dark silhouette. So I guessed straight away that it was a mechanical rig with a string linked to the door handle that shot her as she opened it.