The Black Echo - Michael Connelly (1992) Little Brown 

Twists upon twists in the first Bosch novel.  Bosch is a celebrated and demoted detective in the LAPD.  A dead vet is found in a pipe at the reservoir in Hollywood Hills.  Bosch is able to identify the body as someone he served with in Viet Nam. Bosch sees what others don't and realizes it is not an OD, but a murder - he goes to the man's apartment and finds it has been ransacked, but he comes across a pawn ticket for a piece of jewelry.  He visits the pawnshop and discovers it was robbed the night before, taking the item from the ticket, but there is a picture of the item.  It turns out that both the dead guy and Bosch were looked at by the FBI for a bank robbery that happened while Bosch was on a forced vacation.  The IAD want Bosch so bad they can barely restrain themselves.  This looks to them like a tie-in that they can use against Bosch.  When he braces the FBI for info on the robbery, they call his boss and get him taken off the case, then call back and ask to have him put back on as a liaison to them.  He figures-out that there was a high-up Vietnamese police chief that had a box with no declared value in the first robbery, but as he digs further, there is reason to believe that the man had a fortune in diamonds in his box.  There is another Vietnamese who had diamonds in different bank and he suspects the other man is a target.