You say he, "misbehaves at school but not at home." Yet, you also say, "Parents do discipline and are at their wits end, as we all are." Question is, are the parents disciplining him for what he does at home or at school? He is too young for the parents to discipline him for what he does at school. Discipline must be immediate at this age.
If he is perfect at home, then the school environment is messing him up. I kinda of doubt this. The parents must be seeing some of the same behavior at home - and they need to start dealing with it. There is only so much you can do. Basically, immediate time-outs. Also, start documenting his behaviors. You didn't say when his birthday is, but kindergarten would not be the best idea for next year.
The no remorse is not that unusual. He may have found that showing no remorse messes up the adults. You need to deal with the behavior, not his actions afterwards.
Essentially, the parents may not see him in context with other kids and may not realize how different his behavior is. It might be helpful if they visited the school and watched him. I think it is extremely important that you let the parents know your concerns. It sounds like they need professional help for their child. Lynn Clarks' book SOS: Help for Parents might help the parents (and maybe even you). Good Luck!
there are in his class 10 other kids - 5 girls and 5 boys so total 11 kids, all 5-6 yrs old
in my supervision there are 20-30 kids ranging from kindergarten to 7th grade and varies boy girl ratio mostly even
I am not seeing this repetitive behavior with any of the other children and if any had to got to the principal it stops it real quick - in his case that is becoming the norm and never see remorse even first visit to principal
How many other children are with him, what are their ages, and what is the boy/girl division?