What's the difference between criminal and perpetrator
Simply put, the crimnal is the one who commit crime, and perpetrator is the one who perpetrate, to the real question should be the difference between the act of crime and the act of perpetrate.
Notice people can perpetrate crime, this indicate that perpetrator is broader than criminal. A perpetrator is definitely a criminal, but a criminal may not a perpetrator.
When people commit crime, it's usually about breaking the law. But when people perpetrate some actions like atrocity, torture, abuse, massacre in war or revolution, they may not break the law, sometimes the actions are forced by law, it's not considered crime in sense of judicial law, but it's still kind of evil actions from the perspective of moral law.
If we look at the history, we will find that there are much more people get killed by perpetrators than by criminals. Some examples include the millions of Tutsi people were killed in Rwanda genocide, the six millions Jews died in in Nazi concentration camps, and even more people were murdered by government decrees enacted in some communism regimes.
Criminals are usually judged, convicted and sentenced, while perpetrators are rarely judged, convicted or sentenced by a justice system, because either there are too many them to be judged one by one or it's done systematically and can't find the individual who responsible for the whole thing.