A rights group has accused the Iraqi government of influencing the judges in the Saddam Hussein trial.
The ousted Iraqi president was sentenced to death on November 5 after being convicted for crimes against humanity.
The trial by Iraqi High Tribunal was marred by so many "procedural and substantive flaws" that imposition of death penalty is "indefensible", the Human Rights Watch said adding that the verdict was "unsound".
"The proceedings in the Dujail trial were fundamentally unfair," Nehal Bhuta of the International Justice programme at Human Rights Watch and author of the 97-page report released on Monday said.
"The tribunal squandered an important opportunity to deliver credible justice to the people of Iraq."
"The Iraqi High Tribunal was undermined from the outset by Iraqi government actions that threatened the independence and perceived impartiality of the court.
Members of Parliament and even ministers regularly denounced the tribunal as weak, leading to the resignation of the first presiding trial judge," it noted.
The shortcomings of the trial, for the killings of more than 100 people from the Iraqi town of Dujail, also call into question subsequent proceedings at the tribunal, the report said.