Blackmail, assured by a flaxen cord.
This is how most people who murder or who support murderers get there. Simply put, most of them have to be addicted to lesser sins, and their silence assured by the fear of being found out.
There was a man in the news not too long ago who murdered a college student.
He started with bits of dishonesty here and there, cheating in school and lying to some people in order to get his way.
He got in trouble for stealing some things later on. Drugs were likely involved.
He got into salacious material and committed fornication.
Adultery and rape were not long in following.
His victim decided not to press charges.
Because his evil went unchecked, it kept on growing. He might even have tried to keep up the facade of being a good and decent person--but at some point, through rage or jealousy or guilt incited by his addiction to adultery, he murdered the woman whom he had seduced and tried to hide her body.
Ask anybody who has been in criminal investigations for a long time. When looking for a motive in a murder, the suspects have all practically without exception committed the next most serious crime: adultery. Adulterers have nearly always stolen things before they stole people. Every person who is a thief first cajoled himself to lie. And so on.
The hefty realization that was too late in coming is that by walking the path of infidelity, dishonesty, one is complicit with the (false, idol) god of murder.
People tell themselves otherwise, that it's not that bad or that it's not going to get that bad. Uncontrolled, however, it all too often does.
The role of blackmail in all of this is that the person could have turned his life around and repented at any point. He could have refused to become worse, and use all his life and energies to endeavor to repair the damages caused. Instead, out of fear of being found out or held to account for lesser crimes, he propelled himself to commit the worst.