So, killing IS justified by the religion, the killing of alleged murderers?
Not alleged no, if there is no evidence they cannot be convicted. If there is evidence and they can be convicted but the family of the victim signs a document stating they are willing to forgive the murderer, they can be released. Or the victims family can choose monetary compensation in return for allowing the murderer to be acquitted. Most poor families choose the last option.
I have zero confidence in anyone who calls themselves "scholars" when it comes to religion. Unless, the term "scholar" means he who interprets scriptures to suit the agenda.
Then you won't be surprised to hear that most scholars of Islam do not venture into politics, government or jurisprudence.