Military grand jury will consider charges later this month to decide if there is enough evidence for a trial [GALLO/GETTY]

At least two of the five US soldiers charged in the deaths of three Afghan civilians had kept body parts taken from Afghan corpses and threatened subordinates, according to new documents released by the US army.

Five soldiers - Calvin Gibbs, Adam Winfield, Jeremy Morlock and Michael Wagon, Andrew Holmes - have been charged with premeditated murder. The soldiers are accused of killing three civilians using guns and grenades, in the province of Kandahar earlier this year, even though they faced no immediate threat.

In charging papers released on Wednesday, prosecutors said Gibbs, the most senior of the charged members, was found in possession of "finger bones, leg bones and a tooth taken from Afghan corpses".

Wagon was found with a skull taken from an Afghan corpse.

Investigators said Morlock and Gibbs, in an attempt to derail the investigation, displayed the finger bones while threatening to kill another man "if he spoke about drug use within the platoon to command and law-enforcement authorities", the document said.

Gibbs is also accused of instructing a soldier to "lie to investigators when questioned about [his] platoon's involvement in drug use and the unlawful killings of Afghan non-combatants", the document said.

Investigators said Gibbs also threatened the soldier by saying, "I'm going to send you home by dropping a tow bar on you." Holmes and Winfield have been charged with wrongful use of hashish.

'Sabotage'

Prosecutors allege Wagon tried to get rid of evidence in the case by "obtaining a computer hard drive, and asking another soldier to erase incriminating evidence from the hard drive", his charging paper said.

Gibbs' laywer has said Gibb denies having taken any part in the alleged conspiracy and that the deaths were all "appropriate engagements".

Gibbs was deployed to the Ramrod Forward Operating Base in Afghanistan to find and dispose of fragmentary grenades.

A base spokeswoman has said charges filed against Morlock involve three separate incidents between January and May. However, it was not clear whether all charged soldiers are accused in all three incidents.

Seven other members of the army unit based at Lewis-McChord have been under investigation for the Afghan civilian deaths, but only the five mentioned above have been charged with premeditated murder.

A military grand jury will consider the charges later this month to decide if there is enough evidence for a military tribunal.