Days after former private Steven Green was charged as a civilian in a US court with rape and four murders, four serving soldiers were charged with the same offences, the US military said in a statement that did not name the troops.
Another soldier, apparently a sixth member of Green's former unit in the 502nd Infantry Regiment, was charged on Saturday with dereliction of duty for not reporting the crime in March.
All five were charged with conspiring with Green, who is accused by US prosecutors of going with three others to a house near the checkpoint they were manning outside Mahmudiya, near Baghdad, and of killing a couple and their their younger daughter before raping and killing their other daughter.
A second soldier also took part in the rape, other soldiers involved alleged.
The two other soldiers who went into the house told prosecutors that they did not kill or rape anyone.
The soldiers face further investigation and a hearing to determine whether the evidence merits a court martial.
Documents showed that the rape victim was aged 14, and not over 20 as US officials had said.
Court documents had given the raped girl's estimated age as 25, although US military officials in Iraq say their documents have her as 20.
Her identity card and a copy of her death certificate, however, show that she was only 14. Local officials and relatives had said she was 15 or 16.
Abeer Qasim Hamza al-Janabi was born on August 19, 1991 in Baghdad, according to the identity card, provided to Reuters by a relative.
A copy of her death certificate, dated March 13, gives the same birth date.
She was found at home by a relative on March 12 and had died from "gunshot wounds to the head, with burns", the death certificate, signed by doctor Wael Habib and a registrar, says.
Abeer's sister, Hadeel, who died of "several gunshot wounds", was six.
The killers tried to burn the bodies and house to cover their tracks, relatives and local officials have said.
Nuri al-Maliki, the Iraqi prime minister, has called for a review of US troops' immunity from prosecution under Iraqi law.