Lee E. Ohanian, a UCLA economist, blames President Herbert Hoover for the Depression but with a surprising twist that I've never heard: his pro-labor policy that kept wages too high and encouraged job sharing, which in turn depressed employment. Ohanian says that this was the single most important event that caused the Depression. See this link. Well, let's take this further: Roosevelt's Section 7a of the National Industrial Recovery Act (1933), Wagner Act (1935), Fair Labor Standards Act (1938). That's off the top of my head.

The usual culprits are the Smoot-Hawley tariff and raising taxes.