what should they do? >> we're skating across the bridge here. >> tara johnson is roller-blading through fairmont park in philadelphia with her boyfriend, garrett couples, on may 6, 2000, when their leisurely saturday afternoon takes a turn. >> i glanced over my left shoulder and noticed there was a gentleman sitting on the bridge. >> next thing tara and garrett know, police cars and fire trucks swarm all around them. they're forced off the bridge to a nearby riverbank. >> i remember commenting to my girlfriend that if he does jump, i'm going in. but i don't think that i really believed that i would actually -- that it would come down to that. >> if it does come to that, garrett couples is qualified. he's a medical student trained in lifesaving cpr. and for eight straight summers he's been an ocean lifeguard with a perfect rescue record. >> i've been in the water at least 100 times. >> by now, more than 50