Gotta love those soundtracks for 1970s heist and private eye films -- lots of funk and jazz to accompany the action (or to try to maintain interest when the action is lacking).
British composer Roy Budd turned in a gem for Diamonds, a 1975 production shot in Israel. Robert Shaw plays dual roles and Richard (Shaft) Roundtree is along for the ride. Soul group The Three Degrees sing three selections, including the title theme.
Budd's score, which had a very limited release on LP in the United Kingdom and Italy, is full of jazzy grooves, including the boss-novaish Beauty and the Bass, which you can listen to and download from the link below.
Beauty and the Bass
The Diamonds soundtrack was reissued in 1999 on both LP (with a gatefold cover) and CD by the Cinephile label with this cover:
Copies of the CD version are easily available at a reasonable price. But an even better bet may be a 2011 release from Silva Screen which pairs Diamonds with another Roy Budd soundtrack -- The Stone Killer, a Charles Bronson film.
Soundtracks of both films are also available as downloads.
Here's another sampling of the Diamonds soundtrack, Thief on the Prowl, from YouTube: