He sued: (1) the shooter's doctors, for prescribing him antidepressant drugs and not adequatley monitoring him (a dubious claim); (2) the theater, for not adequately guarding the exit door the shooter came in through (also pretty dubious); and (3) (I'm not kidding, but I wish I was) the movie studio for releasing an "ultra-violent movie" that attracted a psychotic shooter (an absolutely frivolous claim that should get the lawyer sanctioned).
(hahah that would have been a hoot!)