Hi there, for what it's worth; it's pretty vague; here's a copy/quote of two paragraphs from Kevin's Story found on Joy's Blog:
"Kevin’s girlfriend had an older brother, and he and his wife were also there that evening. After dinner, the five of them started playing cards until about 9:45 or 10pm. It was getting late, so they got their jackets on and were standing in the entryway ready to go when they heard something come across the police scanner. (The girlfriend’s mom always kept the scanner on in the background.) They hadn’t been listening closely, but thought they had heard something about kids, some bikes, Tom Thumb, and possibly a mask."
"Suddenly, they see three police cars go flying past on County 75, lights on, and heading east. (Kevin can’t remember if he heard any sirens, but he remembers the lights.) Since there were only three cops in town at the time (Lorenz, Young/Punky, and a new guy they didn’t know), the group realizes something big must be happening. They decide to follow the cop cars and see what’s going on."
It just sounds like, what they heard was kind of vague, however, the story also includes that they then saw the town's three police cars driving by, with their lights on; and I'd guess, it's the combination of what they heard on the scanner, and seeing the three cars go by that caused an interest.
I'm not saying that what was said across the scanner was vague; I'm saying that according to the story, what they heard was kind of vague (scanner on in the background, etc...). The statement by Kevin about thinking that the bikes were stolen, is a bit odd, but, I don't make too much of it one way or the other. If you're new to the story, Joy's Blog is a good place to start. Some on this discussion board aren't too supportive of it; but, some are, and it's good source of general information on this story. Here's a link to Kevin's Story; also at the beginning, there's a little link that says "New Here, Start from the beginning" and that's worth looking at.
http://www.joybaker.com//?s=Kevin's+Story
To clarify a little further; Kevin's story is not that he heard that some kids had had their bikes stolen over the scanner; as stated above, they really didn't know what was going on, but, it got their attention. Later in the story, he mentions that when he saw the kids bikes, he and his girlfriend weren't sure what to do, and that he just figured that they'd been stolen...., so, it's just kind of his way of explaining his thoughts/actions at that time, in reference to having seen the bikes.
Hope that helps.
ps: I hadn't seen Shergal's response when I went to post this.