I shot the sheriff
If you shot the sheriff why have you been helping to find the murderer?
I've been doing this to avoid the blame being put on me.
There are some bad cops out there but you should not kill them. It is bad and could get you shot by other police officers.
I wasn't going to be caught so I did it.
You can't be too sure that you are going to be scot free from shooting someone. Just because you are trying to help, doesn't mean they won't ever suspect you. How about coming clean so the rest of the force can rest easy?