I'm going to keep my neighbor's car ransom
That could be a big inconvenience to someone. Why are you going to do that?
I've been keeping a close eye on his car and I even know the time he's going to come.
It's illegal to hold someone elses property for ransom. Even if you're upset with him that doesn't give you the right to take something that isn't yours and hold onto it.
I don't care about the legal aspect, this is about holding someone accountable for their actions.
I am not sure what actions you are holding him accountable for. Regardless, people cannot hold onto things that do not belong to them.