PvP doesn't need a lot of work other than mechanics that determines the "seriousness" on the issue.
Bloodstains is a good factor as a clue rather than a system that uses scent to stalk offenders
If magic can be involved. It can be a factor of which blood samples are collected to gain more details on whodunnit.
Nothings perfect though... You can pin murders on others using the blood then.
Maybe that sword used to murder could be cleaned off with a cloth, which then is thrown away.