A few things stand out, besides the garter-centric nature of the mystery:
1. Could Tiny have jammed his hat any farther down on his face?
2. This seems like one of the fastest confession-forcings in detective history, even for Inspector Lawson - but you’ll notice the suspect removed his coat, which indicates they were at it for a while.
3. “He kept razzing me about Doris” is your catchphrase of the day. Solution up around 10:30, with two more to come.



Who plays tennis in garters?
Of course today nobody wears garters anyway, but even back then nobody wore garters with tennis wear.
Notice in panel 2 that Wagner's sock had fallen down, indicating a lack of garters. Obviously, Wagner used his own garter to strangle the victim and then put his other garter on the victim's leg to make it appear both were the victim's garters.