How did we fall for the junk science of forensics?

I grew up in the golden age of forensic science, at a time when expert witnesses were becoming celebs, each with their special little area of crimebusting know-how. The papers were full of excited talk about hair microscopy, ballistics and fibre analysis. Crime scene investigators were hot as pop stars.

My brother and I had a nanny with a passion for gore. She wasn’t interested in me as a rule, but I could always hold her attention with a nice chat about blood spatter patterns. We discussed what you could tell from the trajectory of arterial spray or the shape of a drip. Over in America, Herbert MacDonell was the undisputed Blood Spatter King – I think he might have even invented it as a discipline. He appeared regularly on TV with his array of droplet charts, explaining, via PowerPoint, that a round splat meant a vertical drip and that a flatter more tear-shaped droplet meant blood sprayed forcefully at an angle.