Here's a good example of Garrison's theory of propinquity at play. Clay Shaw lived on Burgundy Street in 1960, so Garrison looked at phone directories to see who else lived there.
Mr. Todd, because he lived on Burgundy Street, needed to be investigated. The last sentence is important – Garrison had this belief that one of the gunmen on the grassy knoll had a scar on his face.
Investigating Mr. Todd led to Mr. Bertram. He was now a suspect because he lived across the street from a bar that Clay Bertrand supposedly went to.
None of this went anywhere. But then, this is where propinquity takes you.