He made a direct appeal to the gunman asking him to come forward and explain why he fired the shots and explain to Ms McKee’s family why she died.
The suspect, who police believe to be aged in his teens, appears to be carrying the gun in his right hand in one of the images.
Mr Murphy called on the community to overcome any fears and come forward to identify the main suspect.
“I believe that people in the community know who this individual is. I recognise that people living in Creggan may feel it is difficult to come forward to speak to police,” he said.
“Today I want to provide a personal reassurance that we are able to deal with those issues sensitively.