A man questioned over the murder of Melbourne schoolgirl Masa Vukotic has been ruled out of any involvement in the stabbing.
The man was spotted by traffic police in the area of the Doncaster crime scene, on Wednesday afternoon, and he was apprehended for questioning by homicide detectives.
He was later ruled out of any involvement in the brutal stabbing of the 17-year-old.
"The man bas been released, and is not considered a person of interest," a Victoria Police spokesman told AAP on Wednesday night.
He fitted the description of a suspect seen in security camera footage running in the street moments after the stabbing.
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The footage shows a man, in his 20s, with short dark hair, running away from the reserve after Miss Vukotic screamed.
The suspect carried a white plastic shopping bag in his hand, which may have concealed the murder weapon.
Police are keeping an open mind on what the footage may show as, alternatively, it could show a man running after the murderer.
Neighbours called 000 after hearing Ms Vukotic's screams about 7pm on Tuesday, and she was found by police.
Paramedics were unable to save the Canterbury Girls' Secondary School student.
Detective Inspector Michael Hughes said she had only just left her nearby home and was wearing headphones when she was murdered.
"This is part of her routine, she's been walking daily," Det Insp Hughes told reporters on Wednesday.
"It's terrible a 17-year-old child can't go for a walk on a trail in a park.
"It is an absolute tragedy."
Police haven't ruled out the possibility she was being followed in Koonung Creek Linear Park, possibly by someone local.
They also believe it may have been a random attack, and have warned people in the area to remain vigilant.
Police were doorknocking the suburb on Wednesday night and have been searching the area by helicopter and on foot.
The girl's family have visited the site where she died and were very distressed.
People have been leaving flowers at the reserve.
One local, Greta Engizer, said the park was popular and it wasn't unusual for people to walk alone because it was normally a safe neighbourhood.
"Just when you feel safe, when you feel that Doncaster is a good suburb to be in ... It's really disturbing," she said.
