Minas al-Yusifi, the leader of Iraq's Christian Democrats who had returned from exile in Sweden to reestablish the party, was held by the Iraqi Vengeance Batallion, Martyr al-Isawi Brigade.
They had threatened to behead him unless a $4 million ransom was paid and US troops withdrew from Iraq.
"I have received verbal confirmation from police investigating the case that he has been released," Johansson-Welin, who is in charge of the investigation, said on Friday.
Mosul car bomb
Earlier a car bomb blast killed two Iraqi civilians and wounded 15 others, including six US soldiers, in the northern Iraqi city of Mosul.
The US military said the soldiers wounded in the explosion on Thursday were all in a stable condition. There was, however, no word on the condition of the Iraqis.
Several bomb attacks took
place across Iraq
"The car bomb was driven by a suicide bomber. Two Iraqi citizens were killed. Six US soldiers and nine Iraqi civilians were injured," Sergeant John Franzen said.
Mosul, home to 1.5 million people, has been witness to frequent clashes between US-led forces and their armed opponents since November.
In Baghdad, five civilians, including two children, were wounded in a roadside bomb that targeted an Iraqi police patrol. The wounded were transferred to al-Yarmuk hospital.
Aljazeera learned that two drivers carrying car bombs targeted a US military convoy in the Iraqi city of Haditha west of Baghdad.
Reports said the attacks left casualties among US soldiers but the US army did not comment further.
Aljazeera also learned that the body of an Iraqi police officer, who was kidnapped by unidentified assailants on Thursday night, was found in the southern Iraqi city of Basra.
The officer had been shot dead.