Who is the killer of Mary White?

  It was already half past eight and Mary White just finished her daily shift at the local super market. She closed the doors, cleaned the floor, made the daily report and closed the cash desk. Missis White went to the back room to get dressed and then went out of the shop and locked the door. Mary lived three miles away in a pledged small house, located in a so called ghetto neighborhood, with her husband and their eight year old son. She took her usual way to the near bus station, where she took bus number N45. Five stops away, she got off the bus and greeted the driver. Mary headed through one dark block without even blink with her eye. She was so used to the way, because she worked already 4 years and a half in the market. Missis White heard a strange noise coming from a group of dumpsters, but did not give any attention to it and continue walking. Some meters away, she heard steps behind and this time she made a scared grimace. Mary did not like the neighborhood, because a lot of crimes happened there, but her family could not afford a better placed house. She speeded up the pace and the steps disappeared for a moment. When Mary heard them again she gave a look back, but she could not distinguish a clear image in the dark. The sound of the steps was still there. Her heartbeat accelerated and a dose of adrenaline pumped her body. The sound of the steps was overtaking her. She became more and more scared and almost started running when the steps disappeared once again. Mary was full of emotions. She was sacred and puzzled. The cashier continued walking with a bit of speed. She was still not hearing the harassing steps and this was soothing her. Forty meters away she noticed a strange black shadow on the parallel block. This time a double dose of adrenaline rushed through her veins. She was almost at the end of the next building and she took her look right, surprisingly the shadow disappeared. Missis White heard the steps again. Mary was very scared, so scared that she started running, but a scary shout make her halt. She heard "Don't run Mary". Just one sentence shouted by a man. A lot of questions rushed through her mind: "Who was this guy?", "How the hell he knows my name?" and "Which way should I take?”. Mary tried to keep calm and to get a proper decision. She looked around and then realized that she knew the place, so she started running through the labyrinth of the dark blocks thinking only for the way back to her home. While running Mary took her phone off her pocket and dialed 911. At this moment she saw an illuminated streetlight. She ran to the place and grabbed the pole of the lamp. A voice of salvation came through the phone: