The two were released for lack of evidence, and six other suspects are still being held in Baghdad, a senior Iraqi official close to Al-Maliki said, speaking on condition of anonymity because he was not authorized to release the information.
In the attack Monday, gunmen wearing military-style uniforms stopped the bus at a fake security checkpoint on a remote stretch of desert highway in Anbar. The passengers aboard were all from the Shiite holy city of Karbala in southern Iraq, said Karbala councilman Hussein Shadhan Al-Aboudi, and were headed to the Sayyida Zainab shrine in Damascus, Syria.
Witnesses said the gunmen ordered 22 men off the bus, walked them down the road, and shot them in a nearby valley in Iraq’s Sunni-dominated Anbar province.
The arrests, in turn, stirred Sunni resentments, when a prominent sheik in Anbar accused security forces of “abducting” the suspects as Shiite revenge for the massacre.
Al-Maliki, a Shiite, sought to tamp down sectarian anger.
“It is true that the crime was very ugly, and it caused great pain to the families of the victims, but this attack did not target a specific component of the Iraqi people,” Al-Maliki told reporters. “The terrorists did not differentiate between people, and their goal was to create a crisis.”
Al-Maliki said Sunnis were also killed, but did not elaborate. He confirmed that some suspects had been freed but did not say how many.
Al-Aboudi maintained that all of the bus passengers were Shiite. But he said the same gang of gunmen also killed a Sunni motorist on the same stretch of road earlier that day.
On Saturday, Al-Maliki said the investigation “went through legal channels.” That apparently is what led to the release of the two suspects.
“When they saw that the evidence was not sufficient, legal authorities took a decision on this,” Al-Maliki said. “And we respect the judiciary system.”
Karbala officials who were briefed on the case initially said 10 suspects were arrested. But Al-Aboudi said Saturday that there were only eight, and blamed the discrepancy on confusion in the immediate aftermath of the arrests.
