If you're fully focused on keeping your child safe, don't ever let them get in a car, or get in a body of water deeper than their knees without wearing a life jacket.
I know that sounds silly, but your child is SO much more at risk from those things, than being grabbed by a stranger and murdered. And it must be terrifying in retrospect that you were approached by a serial killer - but you got away is the thing. That's what we need to teach our kids, IMHO - when they sense danger, get away fast. Studies of children who have survived stranger kidnappings show clearly that they knew they were in danger and didn't retreat because they had been taught to obey adults, or it would be socially awkward to turn and run and yell. Strangers don't chase children down who are running away and screaming - they lure them in and get them in quietly. Children should be taught - IMHO - to be bold and not obey someone just because they are an adult. I was a free range child, as probably most were in my generation, and I know the feeling of being approached by someone who means you harm. And I think almost all children can sense that. Not that there aren't some who are literally grabbed while they're walking along, but usually it's a luring process. How many times do we hear communities in an uproar because a few kids in a row have been approached by strangers inviting them into the car? Thank goodness the kids who were witnesses knew to get out of there.