File photo: Robert Bales.

Washington -

The Army prosecutor in the case of a US soldier charged in the shooting spree that killed 16 Afghan civilians said on Tuesday he will seek the death penalty.

Major Rob Stelle argued that Staff Sergeant Robert Bales, 39, should be put to death for committing “the worst, most despicable crimes a human being can commit,” according to the News Tribune in Tacoma, Washington.

Bales' defence team said the Army has left too many questions unanswered about Bales' mental state and challenged the Army's depiction of Bales as methodical in carrying out the killings.

“There is nothing methodical as to what happened here,” said defence attorney Emma Scanlan. She also implied that Bales could have suffered from a head injury or post-traumatic stress disorder or could have been affected by chemicals found in Bales' system, including steroids, alcohol and sleeping pills.

The arguments concluded eight days of pretrial hearings at Fort Lewis, Washington.

Bales allegedly slipped away from his military base before dawn on March 11 and entered homes in a nearby village in the Panjwai district of Kandahar province in southern Afghanistan and shot the civilians, many of whom were sleeping. Nine children were among the dead, and 11 victims were from one family. Six other people were injured.

Afghan witnesses who testified by video link from Kandahar during the hearing described a single US soldier barging into their homes and shooting civilians.

Bales faces several charges including 16 counts of premeditated murder. Bales' commander now will have to decide if there is enough evidence for a trial. - Sapa-dpa