Complex sentence: Montoya, who was blind with fury and had been slowly falling into a deep depression over the past few months, had finally snapped with the loss of Allen and stormed into Corrigan's apparent and after knocking out his girlfriend, Montoya threatened to kill Corrigan.
Split into simpler sentences: Montoya, who was blind with fury and had been slowly falling into a deep depression over the past few months, had finally snapped with the loss of Allen. She stormed into Corrigan's apparent and after knocking out his girlfriend, Montoya threatened to kill Corrigan.