A brilliant inventor devises a purple ray that turns him invisible. He is, of course, betrayed by his associates, goes to prison, gets out, and it's revenge, etc.

But more on Roland West. There was a long-standing rumor that he killed his mistress, Thelma Todd. Wikipedia:

Todd and West began their affair shortly after meeting on a yachting excursion to Catalina Island in 1930. The two eventually became business partners and would move in next door to each other in California. Their relationship was described as volatile and West was described as being controlling and possessive.

Todd was found dead in the garage of her home in December 1935. An autopsy concluded that she died of accidental carbon monoxide poisoning caused by the exhaust of her car. Some conspiracy buffs have suggested that Todd was really murdered by West aboard his yacht, the Joyita. This theory states that he then planted her body in her garage to be found later and staged the scene to resemble an accident.

Supposedly he confessed on his deathbed. Maybe. Then there's the matter of the yacht.