(CNN) -- The Army sergeant accused of leading his men to kill innocent Afghan civilians kept a personal body count of skull tattoos and associated with white supremacists online, according to interviews conducted by military investigators.
Staff Sgt. Calvin Gibbs and four soldiers under his command have been charged with murder in the deaths of three civilian men in Afghanistan. And CNN has learned the Army is also re-examining a 2004 shooting that involved Gibbs in Iraq in which three members of a family were killed.
After his May 11 arrest in Afghanistan, Gibbs showed investigators a tattoo on his lower left leg depicting crossed pistols and six skulls. He told investigators the skulls were a way to keep track of his kills in both Iraq and Afghanistan, according to investigative interview notes shown to CNN.
And a soldier under his command told investigators Gibbs "associates with skinheads online," the investigative notes show. The soldier, who is not charged, told investigators the skinheads "are worse than most gang members I have ever met."
Gibbs is among 12 soldiers from the Army's 5th Stryker Brigade who have been charged in a military investigation stemming from their service in Afghanistan. In addition to the five, including Gibbs, who are charged with premeditated murder, seven more soldiers face charges ranging from conspiracy and interfering in a military investigation to drug use, specifically smoking hashish while in Afghanistan.
The Afghanistan killings took place between January and May, when members of Gibbs' platoon admit they were heavily smoking hashish, some of it laced with opium, according to investigators.
According to investigative documents made available to CNN, Gibbs collected human fingers from his victims. Also, the Army has accused members of Gibbs' platoon of possessing photographs of victims.
Gibbs' attorney has declined comment on the allegations, saying he is still reviewing the case. When contacted at her home, a woman who identified herself as the sergeant's mother also refused to comment.
On Army interrogation tapes obtained by CNN, members of Gibbs' platoon say they fear him.
"I take that man very seriously," said Spc. Adam Winfield, who also faces premeditated murder charges. "He likes to kill things. He is pretty much evil incarnate."
Winfield added, "I have never met a man who can go from one minute joking around, then mindless killings. I mean, he likes to kill things."
Eric Montalvo, an attorney for Winfield, told CNN his client "is not guilty of premeditated murder."
The Army did investigate a fourth killing in Afghanistan involving a man who approached the platoon and refused to follow orders to stop and lift up his shirt. Soldiers fired after the man refused to heed warnings to stop -- which were yelled in Pashto, a commonly spoken language in Afghanistan, according to documents provided to CNN.
And CNN has learned the Army is now re-examining Gibbs' record in Iraq, where he was involved in the killing of an Iraqi family in the summer of 2004.
According to an Army report on the incident, U.S. troops on foot in the northern city of Kirkuk opened fire on a car that approached them, swerving, from behind. Troops feared the vehicle was a possible car bomb, the report states.
When the shooting stopped, two adults and a child were dead and another child was wounded, the report states.
CNN's Courtney Yager, Kathleen Johnston and Scott Zamost contributed to this report.