The Patient (DS George Cross Mysteries #3) by Tim Sullivan

From Atlantic Crime

No fingerprints. No weapon. No witnesses. Can DS Cross prove it was murder?

When a young woman is found dead - with no fingerprints, no weapon, and no witnesses -the Bristol Crime Unit is ready to close the case as suicide, especially after the coroner cites the victim's long history of drug abuse. But her mother is convinced it was murder, saying that her daughter had been clean and sober for over two years.

DS Cross is determined to defy his bosses and re-open the case, even if it costs him his career. Soon he is mired in a labyrinth of potential suspects - but can he solve the case before his superiors shut it down for good?