As tragic as all this is, I never had a problem with my child walking alone in my own, safe neighborhood. When DD(now 18) was 10, DH would put her on a subway in the morning and she would go by herself and get off at her school. A NYC street is much more populated and therefore safer IMO than a lot of semi-deserted suburban areas.
I don't agree. There are so many cubbies, recessed doorways, alleyways, hidden stairwells, dumpsters to hide behind. The many subway entrances are now unmanned as budget cuts have forced the removal of fare booths & the live clerks.
We have muggings, robberies, serial rapists here reported on the news
every day. The anonymity of so many people makes this a perfect place for predators to hide in plain site & blend in until an opportunity presents itself. We have a serial rapist every several months somewhere in the city. We even had a serial subway rapist, who dragged women off the platforms into the secluded areas of the tracks to rape them. There is currently a serial groper on the loose - reaching up women's skirts & groping them. (He better not run into me.

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The technology now is such that there are cameras placed on many street corners & in the subway platforms. But, just as in this case, they document things for AFTER the crime. There are too many street corners and not enough manned monitors to watch every street, every corner, every cubby at every moment to stop a crime at the moment it's happening.
As busy & well populated this place is, there are also lulls in street/sidewalk traffic and isolated pockets of areas to commit crimes. Nabbing a lightweight kid and chloroforming him to pull into a cubby would be easy. Since the Jaycee Duggard details of her snatching came out, I bet copycat chloroformings will be on the rise. It had actually gone out of style as a preferred technique to use.
Yesterday, they showed on the news, camera footage of a mugger who robbed an elderly lady in her wheelchair. Plucked her purse right off her lap, in front of the person pushing her and ran down the street - no one there to stop him. (Lull in street/sidewalk traffic.) Someone recognized him from the footage & reported him. It was a teen. What an idiot he was.
There is a current bill being introduced, called Leiby's Law, after this Brooklyn boy that was murdered. It would create safe havens at various community businesses, who place a sticker in their windows, where children can walk in if they are lost or in trouble and know the workers inside will help them. This way, they don't have to ask random strangers on the streets.
The problem is, it only works if the parents teach their kids about the stickers. The ones who are lax in keeping their kids safe to begin with, may also be the same ones who forget to teach their kids about the stickers, or to remind them until it sticks in their memories to go there when in trouble.