Four men were convicted Friday in the killing of a prominent adviser to Myanmar’s leadership who was shot in the head while holding his infant grandson at Yangon International Airport in 2017.

The killing of the adviser, U Ko Ni, is widely believed to have been a political assassination. But the supposed mastermind has not been found, and what role, if any, the country’s powerful military had in the killing was not revealed in the lengthy trial of the four suspects.

Mr. Ko Ni, 65, was a high-profile lawyer; a member of the governing party, the National League for Democracy; and a Muslim in a predominately Buddhist country riven by religious and ethnic violence. He was also a legal adviser to Myanmar’s leader, Daw Aung San Suu Kyi.

His killing has hindered the governing party’s efforts to change the political system, in which the military that once ran the country as a dictatorship still maintains vast authority.