The fact that after killing his target the troll attacked anyone nearby makes me suspect Lucius, who has no reason to keep any Hogwarts student alive since his son is no longer there.
Between his blood purism, his many allies with children there, and how he de facto rules magical Britain, he has plenty of reason.
Between his blood purism, his many allies with children there, and how he de facto rules magical Britain, he has plenty of reason.