Extra volunteers are being deployed to keep a city parkrun route safe after three people were injured on the course.
The two separate incidents, which involved "youths throwing stones", happened during the Sloughbottom parkrun in Drayton Road during the Marriott’s Way section on November 5 and November 12, according to Norfolk Police.
A police spokeswoman said: "In regards to the parkrun incident, all lines of enquiry have been exhausted and the case has been closed. Of course, we would always review any new information provided to us."
Miranda Ellis, co-event director at Sloughbottom parkrun, said: "There is an overall sense of relief that we can draw a line under this. I hope it will never occur again.
"It has highlighted the importance of volunteer marshals on the course.
"If we have got extra people volunteering we deploy them on extra stretches of Marriott's Way.
"It has raised awareness of something that we hoped would never be an issue. You don't imagine this type would happen. Hopefully it is an isolated event.
"It is business as usual and has not put people off taking part."
The free weekly 5K event, which starts and ends at the Sloughbottom Park pavilion at 9am every Saturday, requires at least six marshals on all sections of the one-lap course.
On November 5 a man was hit in the head and a 12-year-old girl was hit in the leg at around 9.40am in Marriott's Way.
The girl suffered bruising and a man sustained swelling to the head in the incident.
Those who threw the stones ran away and have not yet been caught.
A week later, on November 12 a woman was struck on the arm by an object while running along the same stretch at around 9.25am, according to a Norfolk Police spokeswoman.
They added there were reports of "youths throwing stones" during the first incident and that was the case during the second, according to the Sloughbottom parkrun co-event director.
She added she had spoken to one of the people affected by the attack who were not put off returning.
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