Bahrain used torture, excessive force and fast-track justice in crackdowns on mass protests, according to the findings of a special investigating panel.
Its head, Mahmoud Cherif Bassiouni, also said there was no evidence of Iranian links to Bahrain's Shiite-led protests. That was a clear rebuke Gulf leaders, who accuse Tehran of playing a role in the 10-month-old showdown in the Western-allied kingdom.
The 500-page study - authorised by Bahrain's Sunni rulers in a bid to ease tensions - marks the most comprehensive document detailing alleged security force actions during any of the revolts that have flared across the Arab world this year.
The picture painted in the report also presented a stunning image of a powerful Arab monarch facing a harsh public reckoning, as King Hamad bin Isa Al Khalifa listened to a bullet-point summary of the report's conclusions.
Mr Bassiouni's summary - presented at a royal palace news conference attended by Bahrain's king and crown prince - read like a checklist of complaints by rights groups since February: Middle-of-the-night raids to "create fear," purges from workplaces and universities, jail house abuses including electric shocks and beatings and destruction of Shiite mosques that "gave the impression of collective punishment."
At least 35 people have been killed in violence related to the uprising, including several members of the security forces.
It appeared unlikely that even the strong criticism would satisfy opposition forces, who accused the Sunni monarchy of using all methods at its disposal to avoid sharing power with the nation's Shiite majority. Just hours before the long-awaited report was released, security forces used tear gas and stun grenades in the latest of nearly daily clashes on the strategic island, home to the US Navy's 5th Fleet.
But the inquest was seen as a bold step in a region of monarchs and sheiks who rarely acknowledge shortcomings or face uncomfortable criticism in public.
Bahrain's government promised "no immunity" for anyone suspected of abuses and said it would propose creating a permanent human rights commission.
"All those who have broken the law or ignored lawful orders and instructions will be held accountable," said a government statement, adding that the report notes that the "systematic practice of mistreatment" ended shortly after martial law was repealed on June 1.
Bahrain's Shiites comprise about 70% of the island nation's 525,000 citizens. They have complained of widespread discrimination such as being blocked from top government or military posts. The monarchy has offered numerous concessions - including more powers to the parliament - yet protesters demand that it surrender its command of all top positions and main policies.
"A number of detainees were tortured ... which proved there was a deliberate practice by some," said Bassiouni, whose report covered the period between February 14 and March 30.
The report also was highly critical of a special security court created under martial law that "overtook the national system of justice" and issued harsh sentences - including life in prison and death row rulings - that "denied most defendants elementary fair trial guarantees."
Bahrain has abolished the security court and some of its decisions are under review by civilian magistrates. Mr Bassiouni urged Bahrain to review all the security court verdicts and drop charges against all those accused of non-violent acts such as joining or supporting the protests.
"You found real shortcomings from some government institutions," Bahrain's king told Mr Bassiouni, an Egyptian-born professor of international criminal law and a former member of UN human rights panels.
But the king hit back at finding that Iran did not influence the uprising, saying his government could not provide clear evidence but insisting Tehran's role was clear to "all who have eyes and ears."