Murder Lock: School of the Killing is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

Kotaro Kudo was known as the "Streets' Strongest". Once, 13 thugs, thirsty for revenge, kidnapped his younger sister. Kotaro beat everyone, and on the same night, he was arrested on suspicion of murder, as each of them was later found dead. He is then forcefully enrolled to a certain school, in which all students must meet "a special criteria" to enter..