Death of a Lesser God (Malabar House Series #4) by Vaseem Khan

In the fourth rip-roaring thriller in the award-winning Malabar House series, Persis and Archie travel to the old colonial capital of Calcutta, where they collide head-on with the prejudices and bloody politics of an era engulfed in flame.

Can a white man receive justice in post-colonial India?
Bombay, 1950

James Whitby, sentenced to death for the murder of prominent lawyer and former Quit India activist Fareed Mazumdar, is less than two weeks from a date with the gallows. In a last-ditch attempt to save his son, Whitby's father, arch-colonialist, Charles Whitby,  forces a new investigation into the killing.

The investigation leads Inspector Persis Wadia of the Bombay Police to the old colonial capital of Calcutta, where, with the help of Scotland Yard criminalist Archie Blackfinch, she uncovers a possible link to a second case, the brutal murder of an African-American G.I. during the Calcutta Killings of 1946.
     
How are the cases connected? If Whitby didn't murder Mazumdar, then who did? And why?