Warning follows Pete Hegseth announcement that firing squad execution of Fort Hood killer will be public

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Livestreaming an execution could cause post-traumatic stress disorder in the viewing public, mental health experts have said after the US confirmed plans to broadcast the death by firing squad of a man who shot dead 13 unarmed soldiers.

The US defence secretary, Pete Hegseth, said on Thursday that Nidal Hasan, a former army psychiatrist who killed 13 people at Fort Hood in 2009, would be executed by firing squad on 3 December. Officials later confirmed it would be livestreamed. It is believed it will be the first public execution in the US in almost a century.