Iraqi Prime Minister Mustafa Al Kadhimi says the killers of prominent journalist and commentator Hisham Al Hashimi have been arrested.
Mr Al Kadhimi said on Friday the arrests by security forces had come after warrants were issued to detain the men.
Reports in Iraq said a gang of four men who reportedly carried out the attack had been taken into custody.
State television said one suspect, Ahmed Hamdawi Owayid Kinani, who worked in the Ministry of Interior, confessed to the killing.
Mr Kinani is reported to have shot Al Hashimi using his officially licensed gun.
State TV broadcast brief clips of the apparent confession of the 36-year-old police lieutenant.
Wearing a brown jumpsuit, Mr Kinani confessed to shooting Al Hashimi dead using his pistol. Surveillance footage of the attack showed the men carrying out the killing while riding two motorcycles.
Friday's announcement marks the first reported arrests made over a murder that shocked the country, where killings of activists have surged over the past year.
Al Hashimi was killed outside his Baghdad home on July 6 last year. He left behind his wife, three sons and a daughter.
His killing sparked widespread outrage and protesters took to the streets to demand justice and accountability for his death.
Experts said Friday's announcement was an important development in a case that highlighted issues over factions having impunity to assassinate opponents.
“The government announced the arrest of the killers of Hisham Al Hashimi, without indicating their number,” Raed Al Hamid, a researcher of armed groups in Iraq, told The National.
“The information we have is that the killers are seven people, including an officer with the rank of first lieutenant in the Iraqi Ministry of Interior. This officer has links with the militias.
“It is well known that the Ministry of Interior is always part of the political quota share of the Badr Organisation [an Iraqi Shiite political party and military organisation], but this does not mean that the officer belongs to this organisation,”
The murdered security expert was one of Iraq's most prominent researchers on the country's extremist movements, providing crucial insights into the operations of ISIS and Shiite militia groups.
He was also a supporter of the country's anti-corruption protest movement.
Large-scale demonstrations erupted in Iraq in late 2019, with tens of thousands rallying against government corruption and a lack of basic services and employment opportunities.
After the mass protests, many activists and prominent thinkers like Al Hashimi were killed. The government has been heavily criticised for not acting on these crimes.
A member of the Iraqi Human Rights Commission, Ali Al Bayati, told The National that the development was significant.
“Arresting Hisham Al Hashimi's killers is a positive step towards establishing accountability and ending impunity, but what is most important is to declare the motives of the crime, as it is an unusual crime targeting a public figure and researcher,” he said.
“Other cases of violence in the protests should be brought to justice and hold all perpetrators accountable.”
Al Hashimi had been outspoken against powerful armed groups aligned with Iran. This infuriated Tehran-backed Shiite factions in Iraq's Hashed Al Shaabi grouping of state-recognised militias.
“Al Kadhimi could not name the groups behind it, despite knowing them well,” Mr Al Hamid said.
“I knew Al Hashimi well, and in the last meeting before his assassination, he was talking about threats coming to him from several militia sides.
“He was thinking of moving either to Turkey or to the Kurdistan region, looking for a safe place and to avoid death.”
At the end of May, the government arrested militia leader Qassem Musleh on suspicion of being behind several high-profile assassinations of activists and protesters.
He was later released by the judiciary due to lack of evidence.
“The judiciary did not succumb to any pressure in the case of Qassem Musleh,” a spokesman for Iraq's judiciary has said.
“The evidence is insufficient to convict him, as he was released after being acquitted of the accusation against him of killing protesters, including Ihab Al Wazni,” he said.
“Musleh was not in Iraq at the time of the crime and for this reason he was released.”
Al Wazni was a prominent anti-government campaigner, known as the “Hero of Karbala”, and was killed in the central city by unknown gunmen in May.
* With reporting from Azhar Al-Rubaie in Iraq