In the messages, the agents complained that they had seen abusive, possibly illegal behavior by military interrogators.
He was moved to Nasiriya on June 3 and questioned by military interrogators the next day.
But he also said the group believed that helping military interrogators made a valuable contribution because it was part of an effort to prevent terrorism.
General Sanchez also authorized an investigation into possible wrongdoing by military and civilian interrogators.
He said they were subject to the same regulations as military interrogators and that they appeared "to be doing work up to standard."
"If you're dealing with someone from a cold climate, you'd want to put them in the hottest room possible," said one senior military interrogator.
Some lawyers have complained that military interrogators have tried to drive wedges between them and those they represent.
Rarely do military interrogators get all the language training they need.
By the time the military interrogators were done with him, he had signed a confession that said he was a Communist spy.
In one case, a lawyer said, a military interrogator recently told a detainee that he should not trust his lawyers because they are Jews.