Snapchat’s automated detection software picked up the comment, the company alerted the FBI, and the girl was arrested on school grounds within hours.

Someone should tell the kids about Signal.

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As for monitoring on school computers, that seems OK to me if it’s disclosed to the students and parents in advance. What’s problematic is the responses, which seem much more focused on ass-covering than student welfare. I imagine most 13 year olds have made jokes about killing people once or twice and any adult with common sense would be able to tell they’re jokes.