Knowledge is a dangerous thing. Which is why Alec is asking. It's also a bit invasive, to pick at someone's essence like he will. It won't hurt, but...

Eyes loosing focus, he peers at the space around Zack. The strings that make up his reality. All the connections that make him up. From him to Abe and everyone else he's interacted with. One of them would link to his headaches and then he could follow the string back to who did it. It won't do him any good to undo the problem if it could be redone, after all.