The solution you are looking for is to bring some level of investigation to administrating.
I've been advocating for this for a while now and there is a more fleshed out response in the CA+ section already. Regardless, most of the issues listed get answered with "Well admins can't do anything unless they see it," as you can see from a few of the posts above. Well, why not change that? The logs are an incredible tool to discern rule-breaking on TTT and JB. Someone gets reported you check logs to find out if it's plausible. Then get the accused's attention and ask them for their side of the story. There are many ways to get their attention; psay, csay, slapping, etc. If their side of the story clarifies that this player broke the rules, then it's a slay. If they jokingly lie and say, "I just felt like it," then that's on them, and that's a slay. They can't go back and appeal or complain because their words and their choices led to the slay even if they had valid reason to kill.
The alternative currently is having admins sit in spec for rounds on end waiting for rdm to occur. This can often lead to more problems when the person who was rdmed get’s frustrated with the lack of administration and subsequently revenge rdm’s. Well now that the admin is spectating the accused, the accuser gets slain leading to more frustration from them and to them leaving the server or rdming more.
Now I understand there is still potential for mistakes, but I believe the risk is low compared to the increase in administration. Having to deal with the occasional appeal due to this is not as bad as the countless people constantly getting away with rdm. And even then, perhaps the solution is raising the number of warnings before banning from one to two to add a safety net from these potential mistakes. The number of legitimate punishments going out would still be sufficient to quickly ban rule-breakers despite this increase.
I also loosely advocate for matching the punishment to the crime, meaning, if someone rdms three people in a round, they should be slain for three rounds. They should experience the loss of rounds that those three people experienced. This would still only count as one warning.
I'll avoid going into much more detail than that to avoid making this post any longer. I will say that I haven't seen any solid reasoning against it other than "Admins aren't investigators, so it shouldn't happen." And finally, I don't think this is an idea that can be fleshed out without going over it in a verbal setting as there are many intricacies that can't be discussed easily.
Hopefully, you made it this far and thank you for reading.