KARACHI: Investigators have found no match for casings of bullets that killed prominent human rights activist Sabeen Mahmud, dashing hopes for quick answers to a murder is raising fears for the safety of dissenting voices.

Sabeen Mahmud — Photo courtesy: Flickr

Gunmen on a motorcycle attacked Mahmud late last Friday in Karachi, as she was leaving her cafe The Second Floor (T2F), where she held art exhibitions and talks. She had just hosted a discussion on disappearances in Balochistan, where the army is fighting a separatist insurgency, and, rights workers say, overseeing a campaign of killing opponents.

The army denies rights abuses.

Investigators recovered bullet casings from the scene but drew a blank.

Read: Director T2F Sabeen Mahmud shot dead in Karachi

"That suggests that a new group or new weapon has been used in the killing," a law enforcement official involved in the case, who declined to be identified because the topic is sensitive, said late on Monday.

Police say their only witness is Mahmud's mother, who was with her and was wounded. Investigators suspect the killers had a back-up team of two men on a motorcycle and police are poring over CCTV footage. Investigators desperate for clues are monitoring social media in hopes that loose talk could provide a lead, said another senior law enforcement official.

Authorities had earlier blocked the talk, titled “Unsilencing Balochistan”, when it was scheduled at the Lahore University of Management Sciences (LUMS) earlier this month.

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Mahmud had told friends that officials of the Inter-Services Intelligence (ISI) agency visited her in 2013 to ask about her work and finances, the law enforcement official said.

She had recently asked friends if she should go ahead with the Balochistan talk, he added. The army has condemned Mahmud's killing, saying intelligence agents would help in the investigation. However, human rights workers have not been reassured.

Know more: Intelligence agencies to probe Sabeen Mahmud's murder: ISPR

"There's a lot of fear among the people, about whoever speaks out about Balochistan, what's going to happen," said Rukhsana Shama of the rights group Bedari. "It's easy to point fingers at the agencies but no one knows."

'Third party'

For many here, the separatists in Balochistan pose a more alarming threat than militants. The military says the rebels get help from India, but India denies this allegation.

Security concerns in the province took on added urgency days before Mahmud was killed, when China's President Xi Jinping unveiled projects worth up to $46 billion for an economic corridor anchored there. The army has vowed to crush the insurgency.

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The first law enforcement official said Mahmud's killers might have taken advantage of the tension between the authorities and Mahmud over her Balochistan activism.

"Our hunch is that some third party exploited the standoff," he said, suggesting India.

Security and government officials point fingers at India's spy agency for behind inexplicable violence, but have not produced concrete evidence to support this assertion. This case is unlikely to be solved if any security agency is behind it, the first official said.

Suspicion that Pakistan's intelligence was somehow responsible for the killing, in a bid to silence dissent, is dangerous to national security, said political commentator and journalist Moeed Pirzada.

"It is of vital importance that intelligence agencies work hard to expose the murderers, to restore trust between the state and its most aware citizens," Pirzada added.