Not excusing the killer but let’s be real. Laying your hands on another person during a confrontation can be fatal. If the dead boy had gone to an adult authority and let them handle it he would be alive today.
Just walk away....
People shouldn't put their hands on other people unless necessary, but there is a thing called "proportionality."
The "dead boy" may have committed an offense, but the reaction was neither rational, predictable, or acceptable.
Unless it is in a dark alley or with angry people confronting you en masse, stabbing someone who put their hands on you is a bridge too far even if you don't actually stab them in the chest.
This nasty piece of sh*t needs to be killed and his body should be thrown into a furnace.