How does Mr. Lawrence put an end to the gun battle between Kerris and Elvis, Rossi, and Pike?

Before Rossi, Cole, and Pike can get to Mr. Lawrence, he is shot and left for dead. During the gun fight between Kerris and the others, Rossi notices that he is still alive and making his way toward the gun of one of Green's security guards, who is now dead. Walter Lawrence was behind Kerrris, who is looking at Elvis and Rossi, and shoots him. He gets off several shots until Kerris falls to the ground.