YANGON (Reuters) - Tens of thousands of people gathered in the Myanmar city of Yangon on Monday for the funeral of Ko Ni, a Muslim lawyer shot dead the previous day who was involved in efforts to amend a military drafted constitution.

Supporters carry the coffin of Ko Ni, a prominent member of Myanmar's Muslim minority and legal adviser for Myanmar's ruling National League for Democracy, after he was shot dead, in Yangon, Myanmar January 30, 2017. REUTERS/Soe Zeya Tun

The 63-year-old was an expert in constitutional law and adviser to Aung San Suu Kyi’s ruling National League for Democracy (NLD) party, that came to power in April. He was also a prominent member of Myanmar’s Muslim minority.

His killing, amid heightened communal and religious tension in Buddhist-majority Myanmar, appears to be a rare act of political violence in the former capital that coincided with a tough security operation in a northwestern region populated mostly by Muslims.

Police have arrested a 53-year-old man, suspected to be the lone gunman who shot Ko Ni in the head while the lawyer held his grandson outside Yangon’s international airport on Sunday evening.

He had just returned from a trip to Indonesia, where Myanmar government officials and Muslim community leaders discussed with Indonesian counterparts issues of reconciliation.

Taxi driver Nay Win, 42, was also killed when he attempted to apprehend the gunman, state media reported.

Police Colonel Myo Thu Soe told Reuters the suspect, Kyi Linn, was from central Myanmar’s Yinmabin township who has served two stints in jail for trafficking religious antiques.

Kyi Linn was last released in a 2014 amnesty by then-President Thein Sein, he said, adding that the suspect had not given clear answers during interrogation.

“We cannot say exactly why he killed or who was behind him,” Myo Thu Soe said.

Reuters was unable to contact Kyi Linn’s family for comment and it was not clear if he had legal representation.

An estimated 100,000 mourners, including family members, lawyers, NLD activists and members of Yangon’s diplomatic corps, attended Ko Ni’s funeral beginning at a Muslim cemetery in northern Yangon.

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Suu Kyi was not in attendance and has yet to comment on the killing. Her party said on Sunday Ko Ni’s death was “a great loss for which there is no substitute”.

LEGAL MASTERMIND

Khin Maung Htay, a colleague of Ko Ni’s at the Yangon-based Laurel Law Firm, said Ko Ni was instrumental in devising the role of “state counsellor” for Suu Kyi, enabling her to lead the government.

The 2008 constitution, drawn up by the then ruling military, bars Nobel laureate Suu Kyi from the presidency because she has family members who are foreign citizens.

Ko Ni was working on amendments that would further challenge the role of the military, which retains a quarter of parliamentary seats and controls security ministries under the charter.

Aung Shin, a member of the NLD’s central committee, said the murder was a “well-planned, fearless conspiracy” to kill a man who had extensive legal expertise and an ability to communicate the flaws of the 2008 constitution to the public.

Ko Ni was also spearheading a new Interfaith Harmony Bill that would include provisions on hate speech, hate crimes and discrimination, according to two experts working with him on the draft legislation.

Family members and friends told Reuters that Ko Ni had received death threats connected to his political work, but the motive for the killing was not known.

The timing of the killing was a matter of particular concern, said the International Crisis Group (ICG) think-tank, since it comes just months after deadly attacks on police near the border with Bangladesh blamed on insurgents from the Rohingya Muslim minority.

It was essential “that no stone is left unturned in finding the truth about this incident and who may have been behind it”, the Brussels-based group said in a statement.

The United Nations Office for the Coordination of Humanitarian Affairs said on Monday 69,000 people were now estimated to have fled to Bangladesh since the launch of a sweep by the security forces in response to the attacks on Oct. 9 in which nine policemen were killed.

More than 23,000 people have been internally displaced, the office said.

“In a context of strong anti-Muslim sentiment, rampant hate speech on social media, and virulent Buddhist nationalism propounded by some senior monks, this crime could embolden others and unleash further violence,” the ICG said.