To investigate a matter thoroughly; to inquire deeply into the root cause or origin of something

to pursue something back to its origins; to trace back to the source; to get to the bottom of something

to examine roots and inquire at the base; to investigate thoroughly or search deeply into the details of a matter

to inquire into the fundamental cause of a problem; to investigate the source of an issue

To get to the bottom of a matter; to trace something back to its very root or origin.