[ He wanted to reach out, to make sure she didn't fall over onto the ground, or worse, into the fire. He held himself back, but he did wait until he was sure she was okay before he continued. ]

The Empire is responsible for a lot of... questionable programs, one of which is the Death Trooper program. Stormtroopers that fall under this program are terrifying; no one has ever seen them without their helmet, and they seem to be something other than human. They shrug off blaster fire like it's nothing and are really difficult to kill.

[ Luke paused for a moment, letting out a breath. ]

But there had to be a lot of... 'waste' left over from the experiments that were conducted to make them possible. It's possible the prison ship ran into a ship full of those cast off experiments, and unintentionally brought over whatever failed experiment with them.