It should be James because Jason was eating lunch and Lia's sis was talking to friends which means it was a break. So Jason should not be taking any class.
So James.
Also if I am wrong, I know one thing that Lia's sis is not the murderer/ criminal/ guilty because she has many alibis (her friends)
Lia was a target for many bullies. But today she got pushed off the rooftop and was found ded. The suspects:
Jason: I was busy at eating lunch
Lia’s sis: I was talking to my friends
James: I was in class
Who pushed Lia of the rooftop?