Poul Anderson 
Murder In Black Letter 

This is a Cock Robin Mystery introducing Trygve Yamamura–judo expert, Samurai sword connoisseur and private detective–triple threat to San Francisco crime. These combined skills enable him to keep his own head attached while finding out who removed someone else’s with honorable Japaneses weapon. This is a good old-fashioned detective story, a genuine whodunit, with a good deal of suspense thrown in. (Goodreads)