Free from the small press re-publisher via KDP Select @
Amazon:
The Doppelgänger Gambit by Hugo-nominee Lee Killough (
ISFDB,
Wikipedia), 1st in her Brill/Maxwell series of sci-fi police procedural murder mysteries, originally out from Del Rey in 1979.
It looks like straightforward suicide to Detective Janna Brill. Starship outfitter Andy Kellener locked himself in his office after hours and took a fatal drug dose. But Brill’s exasperating new partner Mama Maxwell thinks it’s murder, and his chief suspect is Kellener’s partner Jorge Hazlett. The trouble is, Hazlett has an airtight alibi. In 2091's cashless society, every purchase is made with a data chip implanted in the individual’s wrist...and Hazlett’s bank records put him in a shopping mall clear across town at the time of his partner’s death. To get their man, Brill and Maxwell have to prove Hazlett faked his shopping spree...and possibly destroy law enforcement’s best tool since DNA for tracking suspects!