How did he know?

Rating: Null/10 (13 November 2017)

How did Michael know who his sister was? He travels directly to Haddonfield and stalks her...hiding in bushes etc...etc... but as explained in the sequel how would he know she was being adopted after their parents died? Dr. Loomis didn't even have that information to pass along to Michael. There's the break-in at the school scene with the knife sticking into the desk..is that somehow the way Michael knew her name? By going through yearbooks? Seems unlikely...Has this ever been brought up before?