The FBI has pushed its use of social media like into new territory to help protect Americans from those who break the law. But there are big risks of damaging ongoing investigations.

This guy was ready to go, had all these weapons, had the propensity to do it — it was just a matter of what day was going to ...

A 22-year-old man who allegedly stockpiled weapons, ammunition and gear with the intent to carry out threats of mass violence ...

A man posing as a sheriff's deputy shared graphic fantasies of violence with a teenager who later killed two at her high ...