The body of Saadoun Sughaiyer al-Janabi was found in the street near Baghdad's Fardous Mosque shortly after his abduction late on Thursday with several gunshot wounds to the head and chest.
Al-Janabi was abducted from his office on Thursday evening, a day after he participated in the first session of the trial, acting as the lawyer of one Saddam's seven co-defendants.
Al-Janabi, who was in the courtroom for Wednesday's opening session of the trial, was dragged out from his office in the eastern Shaab district.
He is one of two lawyers representing Awad Hamed al-Bander, one of seven Baath party officials being tried with Saddam.
The killing was the first set-back for a tribunal that has been held under tight security.
Heavy protection was provided for prosecutors and judges
in the Saddam trial, on the theory that they were likely
targets of pro-Saddam supporters seeking revenge.
Their names have not been revealed and their faces were not shown in the broadcast of Wednesday's opening session, with the exception of the presiding judge and the top prosecutor,
whose identities were revealed for the first time just before the trial.
For months, the Shaab district where al-Janabi was seized has been the scene of attacks on its mixed population of Sunnis and Shias.