Lying prone

The composition writing below originally written by a student has been revised by me. However, I'm not satisfied with it. Please help me correct the errors of it. Thanks a lot.

An Unforgettable Experience
Yesterday afternoon, Peter was waiting in line to see a bank teller. Suddenly a man pulled out a gun. The man yelled for everyone in the bank to fall to the ground or he would shoot, demanding the bank teller to put a lot of money into the bank robber’s bag. However, Peter was very angry. He wanted to stop the robber from robbing the bank and help everyone in the bank out of the woods. The robber pointed the gun at the bank teller and shouted, “Hurry up! Take the money bag to me.” Everyone lying prone on the floor was terrified and nobody had the courage to do anything to fight back. Peter thought he had to find a way to save the people. He tripped the silent alarm to the police without being seen by the robber. After finishing it, what he could do was just waiting for the police. Soon after the bank teller had filled the bag with money, the robber took the bag full of money and was trying to run away. Peter was distraught with worry and prayed for the coming of the police. As the robber was running out of the door, the police rushed to the scene just in time. They shouted an order at him with their guns, “Freeze!” The robber knew that it was hard to escape, so he laid down his arms and the police arrested him. Luckily, nobody got hurt and the crisis was eliminated. It was really an unforgettable experience for Peter.