Forensics is full of gee-whiz-cool csi stuff which eventually is shown to be worthless. Polygraphs are a great example; they're still very wisely used in the US, despite piles of evidence showing they're prone to both false positives and false negatives. Sibling comments saying they aren't forensics because they've been discredited are missing the point: these are typical crime tech, and have been lately discredited, but are still in use in the US regardless.

https://en.m.wikipedia.org/wiki/Polygraph

For a more recent example, here's an article on denim analysis...

https://www.nytimes.com/2020/04/08/science/denim-pattern-mat...

The underlying problems seem to be bad incentives (the prosecution is paid+evaluated on its ability to put people in jail) and the court's willingness to accept insufficiently validated tech.