But the family of Sergeant Robert Bales insisted he was innocent until proven guilty, calling him "courageous and honourable," while his lawyer raised questions about the role of alcohol, drugs and stress in the tragedy.
Wrapping up their case in the pre-trial hearing, prosecutors lashed the "heinous and despicable" alleged massacre in March, details of which were given during an eight-day hearing at a military base south of Seattle.
"Based on the sheer brutality and nature of the crimes, it is our recommendation to proceed to a general court-martial," said prosecutor Major Rob Stelle at Joint Base Lewis-McChord outside Tacoma, Washington.
"Because of the heinous, brutal and methodical (nature of the alleged crimes), we ask that that the sentencing authority have the full range of punishment," including the death penalty, he added.
Bales faces 16 counts of murder, six of attempted murder, seven of assault, two of using drugs and one of drinking alcohol. Seventeen of the 22 victims were women or children and almost all were shot in the head.
The 39-year-old allegedly left his base in the Panjwayi district of southern Kandahar province on the night of March 11 to commit the killings, which included nine children. He allegedly set several of their bodies on fire.
Prosecutors at the so-called Article 32 pre-trial hearing have alleged that Bales left the base twice to carry out the killings, returning in between and even telling a colleague what he had done.
The week-long hearing included three evening sessions -- daytime in Afghanistan -- to hear testimony by video conference from Afghan victims and relatives of those who died.
Stelle said the case should go to a court-martial because "something horrible happened" and Bales was clearly aware of what he had done.
"The most telling evidence we have are the statements made by Sergeant Bales in the few hours (after the incident) -- statements that demonstrate a clear memory of what happened and a clear sense of guilt," said Stelle.
But Bales's lawyer Emma Scanlan questioned whether there was enough evidence for the case to go to full trial, citing possible post-traumatic stress disorder and other medical issues.
"There are a number of questions that have not been answered," she said. "We have been told that Sergeant Bales was 'lucid, coherent and responsive.' But we don't know what it means to be on alcohol, steroids and sleeping aids."
Reported inconsistencies included witnesses talking of possibly two gunmen, and mentioning a shooter with a light on his helmet, while Bales had none. "We need to know if there was more than one person outside that wire," she said.
"We don't know so many things about this case... we ask that everybody keep an open mind as we go forward as we investigate what is actually going on here."
The hearing was held to decide whether Bales should face a full court martial. Investigating Officer Colonel Lee Deneke said he would submit a written recommendation "later this week or over the weekend." A three-star general at the base will then rule on whether to proceed with a court-martial.
In a statement read out by the soldier's sister Stephanie Tandberg after the hearing, the family said it had yet to learn the how, why and what of the incident after the hearing.
"Much of the testimony was painful, even heartbreaking, but we are not convinced the government has shown us the truth, the whole truth and nothing but the truth about what happened that night," it said.
"As a family, we all grieve deeply for the Afghani families who lost their loved ones on March 11, but we must all not rush to judgment.
"In America, due process means innocence is always presumed unless and until a trial proves otherwise. There has been no trial yet, and our family member is presumed by law, and by us, to be innocent."