Iquitos ~ The Past Will Kill by John R. Beyer

Jonas Peters and Frank Sanders team up to solve a string of murders, starting with the intentional and fatal bombing of the Common Grounds, a local coffee shop in downtown Riverside—a usually calm city in Southern California. Dozens are dead after an explosion rips apart the Common Grounds, leaving dozens of others gravely wounded. Frank soon finds himself up to his elbows assisting the bombing victims, especially when he discovers that Jonas was walking to the Common Grounds to meet up with his fiancée, but he never made it. In an instant, all their lives are thrust into a trail of death and destruction carried out by an unknown psychopath.