The shooter, who was masked and held a handgun, has been described as a 5ft 7 man of slim build, who was wearing a black padded jacket, black balaclava and black gloves.
Article source: https://www.huffingtonpost.co.uk/entry/olivia-pratt-korbel-what-we-know_uk_63062a6fe4b0e323a25aefce