If a desperate armed gunman was involved, there would have been life-or-death danger to any one of those 40-50 people who happened to stumble across him. (Remember Ricci and the police officer?)
"A single armed gunman would be pretty unlikely to try to take someone on in that situation...."
A single armed gunman would also be pretty unlikely to abduct a teenager from an upstairs bedroom that she shared with her sister......but that's what we're told happened.
Who says he was desperate? If he was in fact someone known to the family, especially if a teen or college age guy, he had a lot of options: give it up, claim Elizabeth had begged him to sneak out together because she needed to talk,let her go and run for it while everyone's attention was on her, hide and keep Elizabeth quiet with a gun to her head, etc. And if I was out in a wooded area in a suburban neighborhood, with a girl I'd just kidnapped, and heard the voices of 40-50 searchers in the immediate area, I sure wouldn't assume they were all unarmed. I'd have been packing my .357 Magnum if I'd been searching in a situation like that, and I'll bet a number of the searchers were well-armed. Heck, the police were probably happy to have the back-up.