Friday the 13th: A New Beginning

A young Tommy Jarvis stumbles upon a graveyard while walking through the woods on a rainy night, where he witnesses two grave robbers digging up the corpse of Jason Voorhees. Jason rises from the grave and murders the grave robbers before advancing towards Tommy.
Awakening from his nightmare, teenager Tommy arrives at Pinehurst Halfway House, a secluded residential treatment facility. Pam Roberts, the director, introduces Tommy to head doctor Matt Letter. In his assigned room, Tommy also meets Reggie, a boy whose grandfather George works as the kitchen cook. Other teens introduced are kind-hearted Robin, Goth Violet, shy Jake, short-tempered Vic, and compulsive eater Joey. The sheriff brings two more residents, nymphomaniac lovers Eddie and Tina, after catching them having sex on neighbor Ethel Hubbard's lawn. Ethel Hubbard and her son Junior show up and threaten to have the house closed down if the teens do not stop sneaking onto their property.
Vic kills Joey with an axe and is subsequently arrested. Attending ambulance drivers Duke and Roy Burns discover the body. Roy is saddened by the death, but Duke believes that the murder was a harmless prank. That night, punks Vinnie and Pete are murdered by an unseen assailant after their car breaks down. The following night, Billy and his friend Lana are killed with an axe. Panic begins to ensue, but the mayor refuses the sheriff's claim that somehow Jason Voorhees has returned.
The next day, more murders occur when Tina and Eddie sneak off into the woods. Ethel's farmhand Raymond is killed while spying on the two having sex. While Eddie leaves to go wash off in the creek, Tina is murdered. Eddie returns to find her dead, and he too is killed. Meanwhile, Tommy and Pam accompany Reggie to visit Reggie's older brother Demon and his girlfriend Anita. While there, Junior has a fight with Tommy, and he runs off when Pam tries to stop it. After Reggie and Pam leave, Demon and Anita are murdered. At the Hubbard farm, Ethel and Junior are both killed as well.
Pam leaves Reggie at the halfway house to look for Tommy. After Reggie falls asleep, the killer enters and murders Jake, Robin, and Violet. Reggie awakens and discovers the dead bodies in Tommy's room before running into Pam. The killer, revealed to be wearing a Jason-esque hockey mask, bursts into the house and chases them out into the rain, after discovering the bodies of Duke, Matt, and George. Pam rushes toward the barn, chased by Jason, but he is struck by a tractor driven by Reggie. They run into the barn and hide as Jason comes to find them. Tommy comes shortly after and believes Jason to be a hallucination until he is attacked. Together, they get Jason to fall out of the loft window, and he is killed on a harrow below. The killer is revealed to have not been Jason, but was Roy Burns all along.
At the hospital, the sheriff tells Pam that Joey was Roy's son and after seeing him slaughtered, he adopted Jason's identity to kill everyone at the house. She goes to Tommy's room, who awakens and stabs her before Tommy awakens to a hallucination of Jason. Facing his fears, he makes Jason's hallucinations disappear. He hears Pam approaching and throws his bed through the window to appear that he has escaped. When she rushes in, he appears from behind the door, wearing Roy's hockey mask and wielding a knife.

Question: Who's grave was dug up?
Answer: Jason Voorhees