What happened in the failed execution of Christa Pike - and what next?
The convicted killer is in hospital in Tennessee after surviving two lethal injections, in a case that has raised many questions.
US convicted murderer Christa Pike is in hospital and being given "life-saving measures" after Tennessee authorities failed in their attempt to execute her by lethal injection.
The case of Pike, whose attempted execution had already been the subject of a high-profile legal battle, has raised a number of questions.
These include what went wrong, what happens next, and - for opponents of the death penalty - fresh concerns around the suffering of an inmate when an execution does not go to plan.
A review into what happened has been ordered and executions in Tennessee have been halted for the rest of the year, Governor Bill Lee said.
Pike, 50, was sentenced to death in 1996 for the murder of 19-year-old Colleen Slemmer, an attack that was perpetrated alongside her then-boyfriend Tadaryl Shipp.
She was scheduled to be put to death on Wednesday evening, local time. The injections were allowed by the US Supreme Court at the eleventh hour after the legal battle.
Pike was given two syringes of the drug pentobarbital, though her legal team said these failed to stop her heartbeat and that she could still be heard snoring.
Tennessee halts executions after death row inmate Christa Pike survives hers
US death row inmate survives execution attempt after two lethal injections
The Tennessee Department of Correction defended the method it used, saying "the protocol does not allow for additional procedures beyond what was carried out this evening".
The state protocol does not clearly specify what should happen if an inmate remains alive after a second dose, according to the AP news agency.
Authorities have yet to provide their explanation of why the dosage given to Pike proved to be non-fatal, although medical experts have provided theories of their own.
Dr Joel Zivot, a professor at the Emory University School of Medicine, told the BBC he had been retained by Pike's legal team as a medical expert and that Pike probably never achieved a sufficient blood level of pentobarbital to cause her breath to stop or heart failure.
The state correction department added that Pike had been taken to an off-site medical facility.
One of her lawyers said she was "being provided life-saving measures" in hospital.
Her health status is unclear as of Thursday morning.
In his emailed comments to the BBC, Zivot said: "It's very possible that as a consequence of the delay of the beginning of resuscitation she will have a brain injury."
A third-party review has been ordered by state Governor Bill Lee, who said on Thursday that Tennessee will halt executions for the rest of the year.
This could impact any additional attempt by the state to execute Pike in the near-term, if she does regain consciousness. Her current state is not clear.
May Martinez, the mother of Colleen Slemmer who had pushed for Pike's execution to take place, told NBC News the events had been "a mess".
Opponents of the death penalty have similarly been quick to react.
Maya Foa, the chief executive of international legal organisation Reprieve, said: "We cannot know exactly what went wrong, because so much happened behind a curtain – lethal injection relies on secrecy at every stage, to hide the violence of the state taking a human life."
Authorities are yet to say whether they will try again to execute Pike. There is a historical precedent of authorities making a second attempt to execute those on death row.
Meanwhile Shipp, Pike's boyfriend and co-defendant, remains in prison, having been spared the death penalty under state law. He was 17 at the time that Slemmer was killed.
What is the drug pentobarbital?
Pentobarbital is a potent sedative that slows down the body, including the nervous system. Doctors sometimes use it as a treatment for certain conditions, but in high doses it can also be used as a lethal injection to cause death.
Its use in lethal injections came under renewed scrutiny last year after a US federal government review - which took place under the presidency of Joe Biden - raised concerns about the drug's potential for "unnecessary pain and suffering".
His government banned its use in federal executions but that did not bind individual states such as Tennessee, which can choose their own methods.
Why the death penalty is on the rise in US
In recent years, states have found some drugs needed for lethal injections harder to come by, because pharmaceutical companies have opposed the use of their products for such purposes.
The Tennessee Department of Correction has not specifically addressed an allegation from Pike's legal team that the pentobarbital it used was "degraded". Drugs may degrade for a number of reasons, including if it has aged beyond its use-by date and its potency has decreased.
