Translation:A conman and three murderers are in prison.
By the way, the words двое, трое, четверо, пятеро etc. are the only choice when, talking about a group of humans which includes at least one male person, you translate phrases like "these three" or "the other two" into Russian. Examples: Эти трое ничего не знают. Оставшиеся двое займутся приготовлением обеда.
Rascal is more about a sly person or a villain but not about a criminal in terms of the law. And there is difference between killer and murderer. Killer is more wide in meaning. To kill is not only about people, for example dog killer, killer shark, killer flood, but murderer is only about people who kill people without justification or excuse. For example a soldier at war is also killer but not murderer. And crime is called a murder in the court. Of cause a murderer can be named killer, especially if he is a serial killer or slayer if he is a violent one.
Which made me realize that, historically, what looks like the genitive singular after 2 - 4 , was once the nominative dual in ancient Russian. Dual number is a category which is only preserved in Slovenian language, but, in ancient times, was a common feature of Indo-European languages. In most Slavic languages, the dual number forms were replaced by the plural number ones, but, in Russian, the dual nominative was confused with the genitive singular which was identical. The forms originally meant to be in used only with 2 spread onto the next two numbers 3 and 4. I wonder if that was also the case in Serbian.