Nighthawking / Russ Thomas.

Enhanced descriptions from Syndetics:

" Firewatching and Nighthawking are comparable with the best of Michael Connelly's Bosch books and James Lee Burke's Robicheaux novels, and - naturally - Ian Rankin; but there's an elegiac quality here that reminds me of Kate Atkinson's Jackson Brodie titles and the Dublin Murder Squad series by Tana French."--AJ Finn, author of The Woman in the Window

When a nighthawker on the hunt for antiquities instead uncovers the body of a foreign student, Detective Adam Tyler is pulled into a serpentine mystery of dangerous secrets, precious finds, and illegal dealings.

You are a trespasser. You are a thief. You are a Nighthawker.

Under the dark cover of night, a figure climbs over the wall of the Botanical Garden with a bag and a metal detector. It's a dicey location in the populous city center, but they're on the hunt--and while most of what they find will be worthless, it takes only one big reward to justify the risk. Only this time, the nighthawker unearths a body. . . .

Detective Sergeant Adam Tyler and his newly promoted protégé, Detective Constable Amina Rabbani, are officially in charge of Cold Case Reviews. But with shrinking budgets and manpower in the department, both are shunted onto the murder investigation--and when the victim is identified as a Chinese national from a wealthy family, in the UK on a student visa, the case takes on new urgency to prevent an international incident.

As Tyler and Rabbani dig further into the victim's life, it's becomes clear there's more to her studies and relationships than meets the eye, and that the original investigation into her disappearance was shoddy at best. Meanwhile, someone else is watching these events . . . someone who knew the victim, and might hold the key to what happened the night she vanished.