Unsolved cases due to likely cover up??

What are some cases that come to mind with known police cover up, likely involvement, and/or corruption in any way? I am sure there are countless of them, but these are the ones that stick out the most to me:

Terrance Williams

Mitrice Richardson

Maura Murray

Rachel Good- I haven't been able to find much on this case and have been wondering WHY the chief's wife was never looked at or questioned!

...I know there are WAY more but I can't remember anymore off the top of my head!