El Eco Negro = The Black Echo

When Harry Boschformer hero cop bumped from the L.A. homicide desk to the lowly Beverly Hills squadgets the call on a death at Mulholland Dam, he recognizes the corpse as that of a fellow soldier in Vietnam. Together they had searched for Viet Cong in burrows beneath Vietnamese villages, and had both experienced the "black echo" of their own panic reverberating in their ears. Further investigation connects his old pal to an unsolved bank jobstorm drains tunneled into the bank vault.
When Harry and beautiful FBI agent Eleanor Wish uncover the connections between Vietnam and the bank job, both are put in danger by deadly ex-Marines and a powerful insider from either the LAPD or the FBI itself.