After the man was killed, she took a phone out and texted Drew's boo. For reasons unknown, he replied to that number knowing it was Mone. She showed the phone to Drew and Drew kept it. She more than likely knew that Drew was going to be with him and didn't appreciate being threatened earlier. For reasons unknown, Drew decided at the moment he did to get back on the case and heard the phone buzz as he sent the text. He immediately thought the worst and made the kill after getting confirmation from seeing the other phone.