“I’ve wondered if it was used as a lure”
Unlikely. The perv liked boys. I doubt he was trying to attract girls. You wouldn’t use a doll to attract boys.
I don’t know what the significance of a doll in the window is, but I don’t think a perv looking for boys would use one for a “lure”.
A doll in the window might also represent to a child - male or female - that there is a kindly person in the house when, in fact, it's a vile, calculating predator.