Johnny Lewis Beat, Dismembered Cat To Death

Johnny Lewis murdered his landlady and then fell to his death -- but he also viciously took the life of the landlady's cat by beating it to death and DISMEMBERING it in the process ... TMZ has learned.

TMZ broke the story that Lewis -- who appeared on "Sons of Anarchy" -- seemed to be on PCP or meth, because he had exhibited superhuman strength as he fought two neighbors immediately after committing murder.

Law enforcement sources tell us Lewis went wild on landlady Catherine Davis' cat ... kicking and beating the life out of the animal and "tearing it apart." Law enforcement tells us Lewis did NOT use a weapon, but rather his bare hands and feet.

Lewis is the only suspect in the murder and cat killing. We're told cops are confident -- Lewis was the culprit.