She was taken to hospital where she subsequently died of her injuries.
The victim is yet to be formally identified but is understood to be 27 years old.
Masum was pictured on CCTV wearing a duffle coat with three large horizontal lines of grey, white and black, light blue or grey tracksuit bottoms with a small black emblem on the left pocket and maroon trainers.
A witness also reported seeing him wearing a grey hoodie with the hood up.
Sky News has spoken to a shopkeeper who said the victim was pushing a baby in a pram when she was attacked.
He ran over to try and help the woman.
“She was on the ground. I tried… there was me, and another guy, we tried. But looks like she was gone,” he said.
He said he saw the victim the morning she died, with her child.
“The child is very small. I think it must be two to four months, something like that.
“She was walking with them all the time.
“What is he going to do when he grows up without mother?”