The Snake Eater - William G. Tapply

Investigating the murder of a Vietnam veteran, Boston lawyer Brady Coyne uncovers a military conspiracy in this "good, fast read" (Publishers Weekly).
Daniel McCloud may grow marijuana, but as far as he's concerned, that does not make him a criminal. A Vietnam veteran still suffering from exposure to Agent Orange, he's found no help from the government and no relief outside of homegrown grass. When the local police in his small New England town bust him for possession, a friend reaches out to Brady Coyne, a Boston lawyer who usually works with New England's upper class. Brady is readying Daniel's defense when the case is inexplicably dropped. He's just beginning to wonder why when the veteran is found murdered.
McCloud had written a memoir, but the manuscript is nowhere to be found. Someone killed the author to keep it from ever seeing the light of day. As Brady digs into McCloud's time in the army, he finds that this troubled vet made some enemies in the jungle.