The investigation into the murder of Pakistan’s only cabinet-level Christian, Shahbaz Bhatti, has become mired amid suspicions of a possible cover-up, sources said.

Lax investigations, a series of freed suspects and lack of coordination across law enforcement organizations have stalled the case following the March 2, 2011 slaying of the federal minister for Minority Affairs, they said. A trial court in the garrison town of Rawalpindi this month exonerated yet another suspect arrested for his alleged role in the murder.

Rana Masood Akhtar, special judge in Anti-terrorism Court II, freed Ziaur Rehman after an investigating officer told the court that he was no longer wanted in the case due to lack of evidence. Bhatti’s family cited business disputes between Rehman and Bhatti as their reason for suspecting Rehman.

In February police had dropped investigations into another suspect, Abid Malik for lack of evidence. At first, Rehman had fled, managing to escape when police arrested Malik from Lahore’s Allama Iqbal International Airport.

Bhatti’s brother, Paul Bhatti, said the family is not satisfied with the police investigation and authorities’ low level of interest in bringing the perpetrators to justice.

“We thought Ziaur Rehman’s arrest would lead us to the killers of my brother, because the police had obtained an international arrest warrant based on evidence,” he said. “I don’t understand why they issued the request [for an Interpol warrant] if they did not have sufficient evidence.”

Bhatti’s All Pakistan Minorities Alliance has also condemned inaction and lack of seriousness of government authorities.

In June 2011, a trial court released Hafiz Nazar Muhammad for lack of evidence after arresting him for having made threatening calls to Bhatti from Sargodha.

Bhatti was an outspoken critic of the country’s widely condemned “blasphemy” laws. At the scene of Bhatti’s murder, police recovered a leaflet, presumably left by the attackers, asserting that they had killed him for raising his voice against the blasphemy laws.

Officially, police claim that the Taliban were behind the murder, while Interior Minister Rehman Malik has put the blame on militant group Sipah-e-Sahaba Pakistan.

The assailants sprayed 25 to 30 bullets at Bhatti’s car after he came out of his mother’s home in a residential area of the Pakistani capital to attend a meeting of the federal cabinet. The federal government had provided bodyguards for Bhatti, but they were not present at the time of the attack.

The murder came two months after Punjab Gov. Salman Taseer was killed by his bodyguard for supporting Asia Noreen (also known as Asia Bibi), the first Christian woman sentenced to death in Pakistan on blasphemy charges. Bhatti had defied death threats after the Jan. 4 assassination of Taseer, conceding in several interviews that he was “the highest target right now” but vowing to continue his work and trusting his life to God.

“Shahbaz Bhatti’s murder is no ordinary case,” said Napolean Qayyum, who belongs to the Pakistan People’s Party, as Bhatti did. “He represented the minorities in the highest forums of government, was a prominent member of a minority religious community himself and was very vocal against the blasphemy laws.”

He said there was some indication that officials were hesitating to publicize their assessments of the case.

“But given its high-profile nature, it is important that they share the truth,” he said.