While the FBI is investigating whether this matter might be an act of domestic terrorism, no motive has been determined at this time.
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America says it has "identified preparations" for an attack similar to that which killed at least 86, including 30 children, in April.
Despite the rain it will still feel muggy with highs of 22C.
The practice of sending mental health patients far away from friends and family for care has become endemic in the NHS, it has been warned.