A man left the murder trial of a decorated US navy Seal stunned after saying he killed a wounded Islamic State fighter himself – not the accused.

Medic Corey Scott was called by prosecutors to testify at the military trial of special operations chief Edward Gallagher, who is accused of murdering a teenage militant in Iraq.

But while he did say Mr Gallagher plunged a knife into the boy after treating him for wounds, the medic unexpectedly took the blame for the killing, claiming he suffocated him afterwards.

Mr Scott said he held his thumb over the youngster’s breathing tube as an act of mercy because Iraqis would have tortured him to death had he survived.

A prosecutor accused Mr Scott of lying, claiming he had told investigators a different story several times and changed it only after he was granted immunity and ordered to testify.

US Navy SEAL on trial accused of murdering wounded Isis fighter Show all 11 1 /11 US Navy SEAL on trial accused of murdering wounded Isis fighter US Navy SEAL on trial accused of murdering wounded Isis fighter US Navy SEAL Special Operations Chief Edward Gallagher leaves court with his wife Andrea 17 June 2019. He is on military trial at San Diego Naval Based accused of murdering a wounded Isis fighter in Iraq in 2017. REUTERS/Mike Blake US Navy SEAL on trial accused of murdering wounded Isis fighter US Navy SEAL Special Operations Chief Edward Gallagher leaves court with his wife Andrea 18 June 2019. REUTERS/Mike Blake US Navy SEAL on trial accused of murdering wounded Isis fighter U.S. Navy SEAL Special Operations Chief Edward Gallagher, charged with war crimes in Iraq, is shown in this undated photo provided May 24, 2019. Courtesy Andrea Gallagher/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. NO RESALES, NO ARCHIVE HANDOUT Andrea Gallagher via REUTERS US Navy SEAL on trial accused of murdering wounded Isis fighter US Navy SEAL Special Operations Chief Edward Gallagher poses with his wife Andrea. Andrea Gallagher via REUTERS US Navy SEAL on trial accused of murdering wounded Isis fighter U.S. Navy SEAL Special Operations Chief Edward Gallagher, charged with war crimes in Iraq, is shown in this undated photo provided May 24, 2019. Courtesy Andrea Gallagher/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. NO RESALES, NO ARCHIVE HANDOUT Andrea Gallagher via REUTERS US Navy SEAL on trial accused of murdering wounded Isis fighter This undated selfie provided by Andrea Gallagher shows her husband, U.S. Navy SEAL Edward Gallagher, who has been charged with allegedly killing an Islamic State prisoner in his care and attempted murder for the shootings of two Iraq civilians in 2017. Gallagher is scheduled to go on trial Monday, June 17, 2019. (Edward Gallagher/Courtesy of Andrea Gallagher via AP, File) Edward Gallagher Andrea Gallagher via AP US Navy SEAL on trial accused of murdering wounded Isis fighter Former US Army member King Cohn arrives at court to support US Navy SEAL Special Operations Chief Edward Gallagher during the first day of jury selection on 17 June 2019. REUTERS/Mike Blake US Navy SEAL on trial accused of murdering wounded Isis fighter Former U.S. army member King Cohn arrives at court to support U.S. Navy SEAL Special Operations Chief Edward Gallagher during the first day of jury selection at the court-martial trial at Naval Base San Diego in San Diego, California , U.S., June 17, 2019. REUTERS/Mike Blake MIKE BLAKE REUTERS/Mike Blake US Navy SEAL on trial accused of murdering wounded Isis fighter FILE PHOTO: U.S. Navy SEAL Special Operations Chief Edward Gallagher, charged with war crimes in Iraq, is shown in this undated photo provided May 24, 2019. Courtesy Andrea Gallagher/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. NO RESALES, NO ARCHIVE/File Photo Handout . Andrea Gallagher via REUTERS US Navy SEAL on trial accused of murdering wounded Isis fighter Defence attorney Timothy Parlatore, representing US Navy SEAL Special Operations Chief Edward Gallagher, speaks with reporters at a pre-trial hearing. Earnie Grafton/REUTERS US Navy SEAL on trial accused of murdering wounded Isis fighter FILE - This 2018 file photo provided by Andrea Gallagher shows her husband, Navy SEAL Edward Gallagher, who has been charged with murder in the 2017 death of an Iraqi war prisoner. Lawyers for Gallagher are seeking to have the charges dismissed for alleged prosecutorial misconduct. Attorneys for Special Operations Chief Gallagher are scheduled to argue in military court Wednesday, May 29, 2019, that the case against him has been tainted by lies, withholding evidence and conducting surveillance on the defense. (Andrea Gallagher via AP, File) Andrea Gallagher Andrea Gallagher via AP

Retired army major general John Altenburg Jr said: “So you can stand up there and you can lie about how you killed the Isis prisoner so Chief Gallagher does not have to go to jail.

“You don’t want Chief Gallagher to go to jail, do you?”

In response, Mr Scott said: “He’s got a wife and family. I don’t think he should be spending his life in prison.”

Mr Gallagher has been charged with premeditated murder in the boy’s death and attempted murder in the shooting of civilians.

The defence has said Mr Gallagher only treated the prisoner for a collapsed lung and that disgruntled sailors fabricated the murder accusations because he was a demanding platoon leader and they didn’t want him to be promoted.

The US navy released a statement saying it would not drop the premeditated murder charge and that it was up to the jurors to decide the credibility of the witness.

Before the stabbing, Mr Scott said that he and Mr Gallagher had stabilised the sedated prisoner who was wounded in an airstrike and that he was breathing normally through a tube inserted to clear his airway.

The medic said he was shocked when Mr Gallagher stabbed the boy at least once below the collarbone.

He said there was no medical reason for it and that Mr Gallagher then grabbed his medical bag and walked away.

He told the courtroom at San Diego naval base: “I was startled and froze up for a little bit.

“I knew he was going to die anyway, and I wanted to save him from waking up to whatever would happen to him.”

Mr Scott added that no one asked him how the patient died.

Four Seals and one former Seal have taken the stand. Mr Scott was the second to say he witnessed Mr Gallagher stab the militant.

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Several of the Seals also described instances when they said Mr Gallagher had fired at civilians, once shooting an old man.

The seven-man jury is made up of five marines and two sailors – all veterans of war zones.

A two-thirds majority – at least five – is needed to convict and anything less will end in acquittal.

The navy said the jury can convict Mr Gallagher of a lesser charge, such as premeditated attempted murder, which carries a maximum penalty of life with parole. There is no minimum sentence.

The trial continues.