An Arizona robber who murdered six people during a violent two-week killing spree in 1996 was executed by lethal injection on Wednesday, authorities said.
Robert Jones, 43, was declared dead at 10:52 am local time (1752 GMT), Arizona state prisons spokesman Doug Nick told AFP.
He was executed by lethal injection with a dose of pentobarbital, the second execution of a death row prisoner in Arizona this month.
The executions come amid an ongoing controversy in several US states, including Arizona, which have exhausted supplies of drugs used for lethal injection.
European suppliers have refused to supply barbiturates commonly used for euthanizing animals to be used for executions, forcing states to seek supplies from compounding pharmacies outside federal control.
Jones is the 32nd death row prisoner to be executed this year in the United States.
He was given six death sentences in 2000 for the murder of six people during two separate robberies in Tucson, Arizona four years earlier.
He was on parole for burglary when he shot dead two people at a tobacconist shop in 1996.
Two weeks later Jones and an accomplice shot dead three women and a man execution-style during the robbery of a firefighters union social club.