Christa Pike's prognosis still unclear after failed execution, lawyer says

US murderer Christa Pike remains critically ill in hospital and her prognosis is still unclear following her failed execution, her lawyer has said on Sunday.

Speaking to CNN on Sunday morning, Pike's lawyer Stephen Ferrell said doctors were still trying to clear two doses of pentobarbital from her body.

Pike, 50, was sentenced to death following her conviction for murdering Colleen Slemmer in 1995.

She survived two execution attempts on Wednesday, and was transferred to a hospital in Nashville, Tennessee.

Ferrell said: "She's still in the hospital, on a ventilator, critically ill, we really don't know the prognosis yet, and may not know for several days."

He didn't believe she had regained consciousness at any point, adding that he has been receiving updates through her medical power of attorney rather than consulting directly with doctors.

He has not been in to see her. "She is guarded. I'm not sure who may have seen her," he said.

Authorities have not yet said whether they will try again to execute Pike. They have also not offered an explanation for what went wrong. But Tennessee Governor Bill Lee suspended all executions for the rest of the year - and the head of prisons in the state said he would resign on Saturday.

"If she recovers - she may not fully recover - and there may be issues about her competence. I mean, we just don't know any of this," Ferrell said. "We have had no discussions about this. The Tennessee attorney general's office so far has not given us any indications of what their intentions will be."

He called on the governor to commute her death sentence to a life sentence "at the very least". "She has endured a torturous attempt at executing her," he said. "She's spent over 30 years in prison, most of that in solitary confinement."

"We don't know right now - and we may never know - what sort of torture she endured during [her failed execution]."

Pike was 18 when she and her then-boyfriend, Tadaryl Shipp, beat, tortured and killed 19-year-old Slemmer in 1995.

She was sentenced to death the following year after a media frenzy around the killing in Knoxville, Tennessee.

Slemmer's mother May Martinez travelled to Nashville for the execution, which moved ahead despite last-minute legal challenges.

Martinez, who supported Pike's death sentence, told local news outlet WJXX that she "broke down in tears" after finding out it was not successful.

"I think that the state owes me a big apology," she said.

The state's Department of Correction has defended the use of lethal injections, saying "the protocol does not allow for additional procedures beyond what was carried out".

Pike's lawyers previously warned that her medical history and anatomy - including thrombocytosis (a blood-clotting condition) and small veins - meant there was a risk she would experience "unnecessary" pain and suffering during a lethal injection.