On Dec. 4, Staff Sgt. Alberto B. Martinez was found not guilty of killing two New York Army National Guard officers in Iraq -- a rare case of soldier-on-soldier violence in the war and a crime for which prosecutors had sought the death penalty.

The verdict demoralized Army prosecutors. The widows of the two officers appeared devastated, convinced that a guilty man had gone unpunished. And last month, Sergeant Martinez was honorably discharged and returned to civilian life, having publicly proclaimed his innocence and sense of vindication.

However, documents obtained by The New York Times show that more than two years before the trial, while prosecutors were still gathering evidence against him, Sergeant Martinez signed an offer to plead guilty to the murder charges. He offered to be sentenced to life in prison with the possibility of parole, and thereby avoid the death penalty.

''This offer to plea originated with me,'' Sergeant Martinez said in the plea offer. ''No person has made any attempt to force or coerce me into making this offer.''

The offer was swiftly rejected by the general responsible for prosecuting the case.

There has been a rich debate in civilian legal circles about whether charging a person with a crime punishable by death compels some defendants to confess to crimes they might not have committed.

In the Martinez case, the guilty plea offer was also signed by the sergeant's two Army defense lawyers, Maj. Marc Cipriano and Capt. E. John Gregory, who were permitted by Army regulations to sign the plea offer only if they believed at the time that their client committed the crime. The two lawyers later successfully defended Sergeant Martinez at trial.

''They had...