Caught by a Cat: Not a Childrens' Book

Detective Redding is faced with an unidentified, unidentified body in the river. Through good police work and the help of a cat, he identifies the victim and a suspect. but there may be as many as four murderers, and more victims join the first, who is actually the second.
Unexpected twists and shifting suspects, along with unlikely and unwilling allies, bring the dragnet tighter, but it's full of holes.
Only teamwork brings a satisfactory conclusion -- with one last death.