Nigeria’s Shia community has said it will only cooperate with a government investigation into a deadly clash with the security forces if a detained leader is freed from custody.

The Kaduna state government in northwest Nigeria has set up a 13-man panel to investigate a Dec. 12, 2015 incident in which over 300 Shia are believed to have been shot dead by Nigerian troops.

The violence followed claims by the military of a planned assassination attempt on army chief, Tukur Buratai, at a roadblock in Zaria town.

The government panel is due for inauguration this week.

However, the Shia community wants to see a jailed leader – Ibrahim El-Zakyzaky – freed and over 730 missing people accounted for by the military.

Although the group claims that it has “full confidence in and are cooperating with” a probe inaugurated by the National Human Rights Commission (NHRC), it has severe reservations about the state-government body.

“Our conditions to participate in the activities of the commission of inquiry (by the government) include the unconditional release of our leader Sheikh Ibrahim El-Zakyzaky,” Ibrahim Musa, spokesman for the Shia – or the Islamic Movement of Nigeria – told Anadolu Agency on Monday.

Although it supports the NHRC, it does not trust the panel set up by the state government, Musa added.

The group has expressed misgivings about the panel’s composition, saying some had in the past expressed strong anti-Shia sentiments and could not be trusted to be impartial.

“Some had even called the government to ‘go for the jugular’ of the Islamic Movement in the past,” Musa said.

El-Zakyzaky, believed to have been severely wounded by gunfire during the violence, is still being held by the Nigerian government after he was arrested at his home.

“None of his followers, doctor or family members have seen him since the incident,” according to Musa.

The army has consistently rejected accusations it used disproportionate force, with its top officials saying soldiers acted within rules of engagement.

Shia campaigners also want guarantees of safety for anyone who testifies at inquiry hearings – before, during and after giving evidence.

Activists also insist that members in military detention facilities should be released while the remains of those killed should be handed over for proper Islamic burial.

•Text courtesy of Anadolu Agency. Photo shows Sheikh El-Zakyzaky after his arrest by soldiers in December 2015.