( 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 .
Staff Sgt . Gibbs is one of one soldiers charged with killing Afghan civilians . A soldier in his platoon told investigators Gibbs was `` pretty much evil incarnate '' The Stryker Brigade is now looking into his role in the the summer of 2004 deaths of a family in Afghanistan .