Complete History of Jack the Ripper is a very interesting and fascinating no nonsense super accurate page turner.
Don’t dismiss Helter Skelter out of hand. It started me on a lifetime of reading true crime.
Oh, sweet, a second installment of recommendations and I didn’t even have to ask! That sound you hear is me frantically scribbling.
I have to come back when it’s not bedtime and update a bit, but one I’ve read since I started this thread, and enjoyed: The Maul and the Pear Tree, by PD James (whose fiction I’ve always liked a lot). It wasn’t perfect - the conclusion is pretty sketchy and unsatisfying - but I loved the way it was rooted in intricate social/historical detail.
And Never let her go by Ann Rule is also very good.
Thunderstruck by Erik Larson is very good too.
Jerry Bledsoe’s Bitter Blood and Blood Games and While He Sleeps are top notch but not well known.
Many of the ones I’d recommend have already been mentioned but I’ll add: Model Crime by Curtis Gathje