D is for Deadbeat by Sue Grafton

When private investigator Kinsey Millhone agrees to deliver a $25,000 check for a new client named Alvin Limardo, she finds herself embroiled in murder. John Daggett, who presented himself to Kinsey as Limardo, ends up dead, yet the authorities believe it was accidental. Kinsey, though, is convinced he was murdered. It turns out that Daggett killed five people while driving drunk and went to prison. The check was for teenager Tony Gahan, whose whole family died in the accident. Could Daggett's death be revenge for the deaths he caused? Kinsey's has her hands full trying to ferret out the truth.