what in the authors life experience might have been the catalyst for this story?

I would check the GradeSaver site on Harper Lee's biography. Here is a bit of it that shows her life was very related to her novel,

"Lee was only five years old in when, in April 1931 in the small Alabama town of Scottsboro, the first trials began with regard to the purported rapes of two white women by nine young black men. The defendants, who were nearly lynched before being brought to court, were not provided with the services of a lawyer until the first day of trial. Despite medical testimony that the women had not been raped, the all-white jury found the men guilty of the crime and sentenced all but the youngest, a twelve-year-old boy, to death."

Please check out the rest, it is quite interesting. I will post the link below.