It was unsuspected. Just and unfortunate draw of bad luck. They hadn't been looking for anyone specific, just whoever they could get their hands on - fast and easy.
Some cruel, twisted minds were just looking to tinker with the limits of the human body. To see just how far it would go. None involved, of course, were bold enough to volunteer. They wanted to explore this stretch of a theory with no expense to themselves.
And poor Glen just happened to be walking home alone on the night they decided to find a test subject.