Now the B.S. begins

It is not in my personality to let things go. I would contact this detective's supervisor or Chief of Police or County Sheriff regarding the detective's attitude and threats to close the case. If not satisfied here, I would then contact the county DA's office, then the state attorney General's office for assistance, if necessary. This could all be done by phone, and doesn't cost anything except a bunch of time and frustration. Don't let a public servant threaten you or force you to do something that you don't agree with. Sounds like this detective is trying to make this thing go away so he doesn't have to do any more work. Don't quit and don't give up. There's always something else you can do.