What you'll have at the end of this, unfortunately, won't tell you exactly how he was killed.That information wasn't kept, especially in a large battle where many men are being killed or wounded.
There are a number of good histories of the 1st Div. and the Aachen battles.Check with your local library. The one book that comes to mind is "Bloody Aachen" (don't remember the author). If you already have his date of death, a history like that will give you a general idea of what the Regiment was doing and where they were fighting on the day he was killed.