From my readings on the subject, I recall that he was apparently shot after insulting a couple of senior drug gang members who objected to seeing Escobar out drinking in a nightclub so soon after the WC exit.

When Bummer was shot in the leg after only a couple of months, and Lazarus left him to run with another dog, it suited the press no end: Bummer was said to be feeling the sting of ingratitude at the desertion of the cur he had saved from death.