Legal challenges are expected after the botched execution of a prisoner on death row in the US state of Oklahoma.

A lethal injection failed to kill Clayton Lockett and it took more than 40 minutes for him to be declared dead from a heart attack.

This is the second time this year that an inmate has gasped for air during a lethal injection.

Many pharmaceutical companies now refuse to supply drugs designed for use in US death chambers.

As a result, state authorities are acquiring the drugs elsewhere, raising suspicions about drug quality and regulation.

Al Jazeera's Shihab Rattansi reports.

Source: Al Jazeera