I'm not in anyway defending what this detective has done, but I will tell what happen to me and why the good detectives sometimes leave the department.
I was ripped off by a thug that drove a large tractor trailer rig. He was so bold he would drive into the job site hot wire a forklift, load up what he wanted and drive off.
The way he got caught was a policeman driving by at 3 am saw something that wasn't normal to the average person driving by. This thug was loading a large wood beam on top of a load of concrete blocks he had stolen off another job. (he got greedy).
When the officer stopped and questioned him the thug confessed and told them how he was doing the crimes.
The way I was brought into this was, he had stolen my stuff earlier in the night and he told the officers where to go find it.
The detective asked me to come out and ID the merchandise, and when I arrived he and I got into a discussion about the crime spree.
The detective informed me this was his last case, he was quitting after 10 years on the force.
I asked him why?
He told me that the prosecutors would not prosecute the crimes.
The detective went on to tell me that this thug would be out on the street before he finished the report on this crime. And that the felony charge would be reduced to a mistaminor!
So the detective was quitting because he felt like he was being betrayed by the prosecutors not doing their job.

We need to drain the swamp! Sorry for the long comment.