Leaving them in a jail cell is not really a good thing to do. Jails are usually used to stop them fron shooting, running away, etc. Otherwise, they can just Alt-Tab to YouTube for a few mins or DC and you'll be none the wiser if you are out and about doing something else.
I understand your concern with wanting to avoid to kick people. What I used to do was Admin Sit with the person who called for Admin Help and the Suspect, after hearing the story, i would tell the suspect that I would keep an eye on him and that no punishment will be given at that time. Now, this will make a lot of people angry with you. I've had people spread around that I allow RDM and NLR under these same circumstances. It's good that you want to keep as many people on the server as possible, but there comes a time when you have to do it because there are people who will RDM, Prop Kill, and abuse basing, and they know how to get around you. I've played with those kind of people, I've even been that type of person. I was able to prop-kill over 100 people in the course of two hours during a stream because I know how to out-smart staff. Watch LostInPlace or MontgomeryBurns to see what I mean.
You can be the nice admin that never kicks and takes your time with every person to explain everything in hopes of changing them, but this will lead to:
1) No roleplaying time. After building up that reputation, people will PM you to help with admin situations and even message you when you are playing a totally different game.
2) People will hate you. If you're the only admin on the server and you are taking your sweet time with everyone, people will call you lazy and a bad admin.
Yes, you are there to help the players, that is what you signed up for when you became an Operator. However, if and when people start to /pm you for admin help, you need to tell them to use "@".
Try to find some balance. That's pretty much all my advice. However, look where I am now. xD So maybe get another reference.