Complex sentence: Sue Hart's second husband was veterinarian Toni Harthoorn whom she was knowing from college days and who was notable for the development of the M-99 (etorphine hydrochloride) capture drug and its accompanying gun, the capture gun, for darting big game animals.
Split into simpler sentences: Sue Hart's second husband was veterinarian Toni Harthoorn whom she had known since college. He was notable for the development of the M-99 (etorphine hydrochloride) capture drug and its accompanying gun, the capture gun, for darting big game animals.