A lawyer representing the first death row inmate likely to be executed in South Carolina since 2011 has decided that he should die by lethal injection after the prisoner refused to choose between three different killing methods, saying that to do so would be “akin to suicide”.

Freddie Owens is now set to be executed using a fatal dose of the sedative pentobarbital. The prisoner had been given until Friday to decide between the three execution methods: lethal injection, the electric chair and the firing squad.

Owens had joined other death row inmates in objecting to both the electric chair and firing squad as cruel and unusual forms of punishment banned under the US constitution. He had also objected to signing the form that would decide between the three techniques on grounds that to do so would mean he were participating in his own killing – equivalent to suicide, he said, which is forbidden by his Muslim faith.

In the absence of a decision from the prisoner himself, Owens’ defense lawyer, Emily Paavola, to whom he had granted power of attorney, stepped in. She knew that if she failed to meet the Friday deadline, South Carolina would by default kill her client by electrocution; in that invidious position, she opted instead for lethal injection.

In a statement, Paavola said: “I have known Mr Owens for 15 years. Under the circumstances, and in light of the information currently available to me, I made the best decision I felt I could make on his behalf.”

Owens was sentenced to capital punishment for the 1999 murder of a petrol station worker, Irene Graves, during a string of robberies. He is the first of five prisoners who have exhausted all their appeals and now face execution after a period of 13 years in which the state’s death chamber has gone unused.

Much of that delay was caused by the difficulty South Carolina has had in procuring lethal injection drugs, given a global boycott by pharmaceutical companies unhappy with their medical products being used to kill people. The state has adopted tight secrecy laws that prevent the public from knowing where it is obtaining its lethal drugs.

Owens’ defense team is now hoping that it can delay the pending execution through last-ditch legal challenges. The lawyers are protesting that the state has provided insufficient information about the quality of the pentobarbital it plans to use, arguing that there could be dire consequences for the prisoner should the drug be faulty or ineffective.

His attorneys are also asking for the execution to be postponed to give more time for new evidence to be considered in his case. In a motion lodged with the state’s supreme court, they argue that a plea deal that was offered to Owens’ co-defendant has come to light that puts his conviction in doubt.

Steven Golden, Owens’ friend who was involved in the robbery, was the only eyewitness to the murder, and there is no other forensic evidence. The motion says that Golden was offered a plea deal whereby he would avoid the death penalty or life in prison without parole if he testified against his friend – a crucial detail that was withheld from Owens’ lawyers at trial.