Even with an exceptionally well trained team of detectives, getting a 90%+ clearance rate seems very suspicious. It is more likely that rather than having better detectives then than we have now, it's that the police now have to go up against better science and technology that can help keep innocent people from being convicted. Bank teen the police just needed to take a few pieces of evidence and create a believable story from it, but now they need that story to match DNA, surveillance, and the right size glove.

Cops in the past were still cops. They didn't care about accurately solving a murder of a poor person, they just wanted to be able to find someone they could punish for it so they could move on to the next thing.