He could have removed the mask at some point. And Jacob at some point had the opportunity to run. I just think it's one possible scenario, Idk. JMO
This was my conclusion right after we were introduced to DH. I felt that it was quick, that it was very local and that Jacob died from gunshot wounds. I think J.E.W. flipped the script on DH and it got out of control, but that is my conjecture for now.