So, who killed the Gradys?

I just watched the Shining, and I'm wondering, who killed the Grady
girls? Was it Jack or the Grady Father. I think that on wikipedia it
said that their father killed the family, but if the father of the
Gradys says that Jack has always been the hotel keeper or whatever,
then wouldn't it be Jack who killed them? After all, they died with an
axe and Jack swings the axe to kill his own family. I think that it's
more Jack, but really want to be sure. So who killed the Grady girls?