Vilseck, Germany (CNN) -- The military released 77,000 of about 87,000 detainees locked up during the Iraq war because there was not enough evidence to hold them, CNN has learned.



"In most cases, if we don't have anything, eventually they'll be released," said Brig. Gen. David Quantock, who oversees detainee operations in Iraq.



Quantock said "many cases are driven purely on intelligence."



"Intelligence does not win a fight in a courtroom. It doesn't win the fight in a courtroom in the United States. It doesn't win in Iraq."



According to the U.S. military, 76,985 detainees have been released out of the 87,011 captured during the Iraq war.



A CNN investigation found that frustration over the Army's policy on detainees may have led to the 2007 killings of four Iraqi men by three decorated Army sergeants at a Baghdad canal.



Former 1st Sgt. John Hatley, who led the mission that day, told CNN in a letter that the detainee policy has "extensive flaws" that repeatedly frustrated soldiers.



On Army interrogation tapes obtained by CNN, other soldiers complained about the Army rules for evidence gathering.



Despite the high release rate, Quantock said he has confidence soldiers can take basic evidence from a crime scene in Iraq.



"We're asking them to take basic evidence, which they've been trained to do," said Quantock, who oversees detainee operations in Iraq. "We've got the greatest soldiers in the world. And I don't accept that they can't take basic evidence off of a crime scene."



CNN asked Quantock to explain why, if it were so easy to collect evidence, so many detainees have been released.



"It took us a while to realize, it goes back to my point of we were trying to make the fight fit the Army as opposed to have the Army fit the fight," Quantock said.



"I think a lot of times we thought the insurgency would dissipate, we were working closely with the government of Iraq, we were trying to improve the Iraqi security forces, but at the end of the day, it didn't work out very well. We had to get better at taking evidence off the crime scene."



A January 9, 2005, memo imposed detailed standards of evidence soldiers needed before taking in suspected insurgents in Iraq. Quantock told CNN the rules detailed in the memo were in effect through the end of 2008.



The memo spells out that evidence of criminal activity should include photos of "physical evidence," "the detainee at the crime scene or place of capture," as well as photos "of the detainee next to the evidence." Other evidence should include "statements written by first-hand witnesses to the criminal activity," the memo states.



At the start of this year, the rules got even stricter. A security agreement with the government of Iraq now requires an arrest warrant signed by an Iraqi judge to detain someone.



Asked about the killings at the canal, Quantock told CNN: "There's never an excuse to execute anyone. They become judge, jury and executioner."
Frustration over detainee policy may have led to what? Four Iraqi detainees were killed by whom?
the 2007 killings of four Iraqi men by three decorated Army sergeants three decorated Army sergeants
question: Frustration over detainee policy may have led to what?, answer: the 2007 killings of four Iraqi men by three decorated Army sergeants | question: Four Iraqi detainees were killed by whom?, answer: three decorated Army sergeants