Supporters of the method say it’s foolproof – but forensic experts say it can be ‘excruciating’ amid allegations it’s been intentionally botched

The tangled path of US capital punishment takes a new turn on Wednesday as Idaho becomes the first state to adopt the firing squad as its primary form of execution, embracing the brutal killing technique even as concerns grow that it can inflict excruciating pain and suffering.

The state’s department of corrections (IDOC) says it has met its deadline, set by the legislature, to have its death chamber at a maximum security prison south of Boise retrofitted and open for business by 1 July. It has spent more than $1m in the venture, including $24,000 on a rack of AR-style, .308-caliber, scoped rifles that will be wielded by volunteer marksmen.