Special Operations Chief Edward Gallagher, a decorated career combat veteran, has denied all the charges and says he is wrongly accused. He could face life in prison if convicted in the trial arising from his 2017 deployment to Mosul, Iraq.
The proceedings in a military courthouse at U.S. Naval Base San Diego are due to last three weeks, starting with the selection of between five and 15 active-duty Navy officers and enlisted personnel to hear the case and render a verdict. Empanelling the jury is expected to take one or two days.
The opening of the trial was postponed several times by a lengthy round of proceedings to deal with defense allegations of prosecutorial misconduct.
Gallagher's lawyers sought dismissal of the charges after learning that Navy prosecutors had electronically tracked email communications of defense lawyers without a warrant, ostensibly to pinpoint the source of material leaked from sealed case files.
The presiding judge, a Navy captain, ultimately removed the lead prosecutor from the case and freed Gallagher from pre-trial confinement.
The judge also granted defense lawyers a potentially valuable edge in jury selection - the right to reject, with no reason given, two more potential jurors than they otherwise could exclude through the use of a "peremptory challenge." Gallagher, 39, is charged with murdering a wounded, helpless Islamic State fighter in his custody by stabbing him in the neck, and with attempted murder in the wounding of two civilians - a school girl and an elderly man - shot from a sniper's perch.
He has pleaded not guilty to all charges, including obstructing justice in the case. He maintains that fellow SEAL team members who are testifying against him, several under grants of immunity, are disgruntled subordinates who fabricated allegations to force him from command.
Before he was released from custody late last month, Gallagher had been ordered restricted to base at the nearby Naval Medical Center San Diego.
He was transferred there in March from a military brig at the Marine Corps Air Station Miramar in Southern California at the direction of Trump, who ordered that Gallagher be held in less-restrictive pretrial confinement "in honor of his past service to our country."
Trump said last month that he is considering pardons for a number of military service members accused of war crimes, and Gallagher's case was believed to be one of those under review.The prospect of presidential clemency seemed heightened by last month's appointment to Gallagher's defense team of Marc Mukasey, one of Trump's personal lawyers. Gallagher's lead civilian attorney, Timothy Parlatore, has said his client has not sought a pardon.