Fifteen of the kidnapped Iraqis were found wandering in eastern Baghdad, many of them showing signs of torture, police and defence officials said on Wednesday.
Police found eight of them together on a major north-south highway in east Baghdad. Patrols were alerted to search for others and another seven were found around the area, three of whom had bullet wounds in their legs.
Al-Kindi hospital confirmed that 13 people had been brought in by police for treatment.
The defence ministry had earlier confirmed the release of two others.
Fifty people were kidnapped in a raid in daylight by armed men dressed in commando uniforms on al-Salhiya street in central Baghdad. About a dozen trucks were used to take them away, including two painted in distinctive commando camouflage style.
Iraq freed hundreds of prisoners
to help 'national reconciliation'
The interior ministry has announced an internal inquiry into the kidnapping, which initially was believed to be an official raid by the ministry's security forces.
Meanwhile, in continuing violence four police officers were killed, and another wounded, on Wednesday when armed men attacked their patrol in Baghdad.
Police sources said the attack took place in the western al-Mansour district of the capital.
Also on Wednesday, more than 590 prisoners were released across Iraq, Iraqi state television said, after Nuri al-Maliki, the prime minister of Iraq, said 2,500 would be freed to help national reconciliation.
Al-Maliki, who has pledged to heal sectarian wounds and crush a Sunni Arab uprising, said on Tuesday that those who had no clear evidence against them or had been detained mistakenly would be released.
When his cabinet took office, al-Maliki said the release of those imprisoned without a just cause would be one of his priorities.
Meanwhile, Italy has confirmed that its troops will leave Iraq by the end of the year.
Massimo D'Alema, the Italian foreign minister, announced the decision during a news conference with Hoshyar Zebari, his Iraqi counterpart, on Wednesday.
D'Alema arrived in Iraq two days after an attack near the southern town of Nasiriyah killed one Italian soldier and wounded four.
Italy's new government has announced plans to reduce the number of Italian soldiers in Iraq to 1,600 from 2,700 this month and to pull out the rest by the end of the year.