Retired judge VR Krishna Iyer wrote to the Gujarat Chief Minister to wish him a happy birthday on Tuesday and, in his letter, described Mr Modi as "someone of nationalistic virtue with global dimensions," the Gujarat information department said in a statement released late on Wednesday evening.
In 2002, Justice Iyer had led a citizens' panel to investigate the communal riots and, in a two-part 600-page report, had alleged that the carnage, in which hundreds of Muslims were killed, was "organised crime perpetrated by the chief minister and his government."
Now, says the government release, the former judge writes, "I am committed to socialism. And I support Mr Modi because he is also a socialist and encourages Gandhian values - protection of human values and rights, brotherhood, justice at social, economic and political field."
He has also reportedly said that "in the chair of the Prime Minister, Mr Modi will fulfil hopes and aspirations of the people of India and uphold national dignity." Mr Modi was chosen the BJP's presumptive PM last week.
The release quotes Justice Iyer as saying that Mr Modi is getting support at a national level for his "good administrative skills and is quite capable of realising the great principles of Swaraj." He has also reportedly expressed confidence that Mr Modi will remove poverty from India.
It was before Justice Iyer's tribunal that Gujarat minister Haren Pandya, who was later assassinated, had deposed that in a late-night meeting on February 27, 2002 - the day the Godhra train attack occurred - the Chief Minister had allegedly asked police and administrative officials to let Hindus vent their anger.