The good news is that he isn't dead. The bad news is that we can't interrogate a sleeping beauty.
We need something to keep him from moving before we wake him up.
There doesn't seem to be any duct tape nearby, so you'll need to make do with good-old rope.
You may have seen some earlier - if not, think of places where it'd make sense to tie a rope.
On the tower's roof, a rope is tied to the right side of the railings.
Good luck untangling all those knots!
Use the 'boy scout guide to knots' to free the rope.
You can then use it to tie up the alien.