Heat Lightning by John Sandford

BCA agent Virgil Flowers is called to a murder scene in New Ulm with a lemony twist. Agent Davenport, his boss, is busy with other problems and Flowers has free rein to hunt the murderer down. Clues lead to an atrocity that happened during the ending of the Viet Nam war. It seems that someone is killing the men that were involved in the murder of a Vietnamese family. Sandford does a great job with characters and dialogue, a great read.