Good grief, that is awful! That poor mum! I remember when I had ds (8 years ago on Friday) that we were warned about exactly this type of incident, so I always strapped ds in. BUT, when I had dd 3 years later, I had a new pram and the carrycot had no straps. She was never strapped in whilst in the carrycot.
You have to worry about the would-be-kidnappers though - how desperate must they be to try this.