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Next week, don't miss our special four-part investigative series, Killings At The Canal: The Army Tapes, about U.S. soldiers who were convicted of murder on the battlefield.

Three sergeants used their service pistols to execute four Iraqi men they had in custody who they believed were insurgents. Questions have emerged: On the battlefield, is murder a crime? And is the Army’s policy on detainees realistic for its soldiers in the battlefield?

While many were focused on the outcome of the presidential election, courts-martial were underway at a U.S. Army base in Germany. Ultimately three army sergeants were found guilty of the execution-style murders of the four Iraqis their 13-man unit had detained. The soldiers were certain the Iraqis were insurgents who had been shooting at them. But under Army rules for holding detainees, they knew they could not meet the burden of proof - and they feared the suspects would be released only to be shooting at soldiers again. So the sergeants made a decision: bypass the detention center, take them to a canal, and kill them.

We have obtained almost 24 hours of interrogation footage which includes a confession from one of the sergeants.

CNN's investigative correspondent Abbie Boudreau and senior investigative producer Scott Zamost also shine a light on the U.S. Army’s policy about how to handle detainees, a policy that was a response to the abuses of Abu Ghraib. Some say it puts an undue burden of proof on U.S. soldiers.