He stopped the outbreak entirely by accident. For all he knew, registering the domain name being queried by WannaCry could have caused the malware to start del

He stopped the outbreak entirely by accident. For all he knew, registering the domain name being queried by WannaCry could have caused the malware to start deleting all the data with no chance for recovery. Even if he did know that he was going to stop the outbreak, it doesn't excuse the fact that he helped create tools that he knew were going to be used for illegal activities.