A convicted child killer executed in Tennessee showed signs of "sustained cardiac activity" two minutes after he was pronounced dead, his lawyer has claimed.

Byron Black, who shot dead his girlfriend Angela Clay and her two daughters, aged six and nine, in a jealous rage in 1988, was executed in August by a lethal injection.

Alleged issues about his case were raised on Friday as part of a lawsuit challenging the US state 's lethal injection policies, amid claims they violate both federal and state constitutional bans on cruel and unusual punishment.

The latest proceedings in Nashville were held to consider whether attorneys representing death row inmates in the lawsuit will be allowed to depose key people involved in carrying out executions in Tennessee.

The court heard that concer

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