There's been a breakthrough in the hunt for a man who attacked a 9-year-old boy in a Balga park, with police releasing a video of a man who may be able to help their investigation.
A 9-year-old boy and his brother were playing at Barry Britton Reserve on Monday afternoon when they were approached by a stranger at around 3.30pm.
As they walked away, police say the man grabbed the boy on the arm before striking him on the face.
"My daughter noticed this old guy running across the reserve and she said, 'oh, he's been up to something'," a witness, Lynette, said.
"Further down there were two boys running across to their home."
Concerned for the youngster, local resident Lynette followed.
"He was hit in the cheek and and his cheek was all red, and he was crying," she said.
Lynette saw another passerby follow the man, but he lost him on Emsworth Way, one block from the park.
The Balga Avenue park is popular with local families, especially on school holidays.
Seven News understands the boys were in the care of an aunt who lives nearby.
Detectives are now hoping the man in this clip comes forward.
Anyone with information is urged to call Crime Stoppers on 1800 333 000.