An injection of chemicals used to execute death row inmates can cause such excruciating pain that veterinarians are banned from using them to put down animals.
That's the claim of one of the most thorough reviews ever undertaken of the administration of the death penalty in the US.
The report urges that inmates be killed with a single chemical overdose, rather than the "three-drug cocktail" used in a series of botched deaths, including Oklahoma's execution of Clayton Lockett last week. His attempted execution, which took one hour and 44 minutes from when he was first restrained on the gurney, caused global outrage.
The report published by the Constitution Project, a Washington-based think tank, has authority because it is endorsed by former judges and police chiefs.
The panel argues that the so-called "three-drug method", in which death row inmates are given a drug combination which, in turn, induces unconsciousness, causes muscle paralysis and stops an individual's heart, "poses a risk of avoidable inmate pain and suffering". A concern with such cocktails is that if the first, anaesthetising drug fails, as has been known to occur, a patient is at risk of feeling the effects of the follow-up drugs.
Instead, the report urges states to adopt a "one-drug protocol" that kills an inmate with a single, high dose of an anaesthetic or barbiturate.
It refers to Tennessee's Nonlivestock Human Death Act, which bans vets from using a certain combination of drugs to euthanise animals on the basis it can cause suffocation by paralysis while the animal is awake.