To be on edge means to be tense, nervous and irritable, and in this context the people are left on edge because of the mind-sick violence.
Consider the staetement "Lawlessness prevailed, the kind of mind-sick violence that left people tense, nervous and irritable.". Based on this statement, is "Lawlessness prevailed, the kind of mind-sick violence that left people on edge .”" a true statement? Yes/no/unknown