Police are now questioning five teenage boys about an alleged gang rape in Melbourne's north.
Up to 10 young men attacked two 15-year-old girls in Roxburgh Park in October.
Two 16-year-olds boys and a 15-year-old handed themselves in to police this morning.
Another 16-year-old boy and a 17-year-old have now gone to police.
Detectives believe the attack was planned, although the victims did not know their attackers.
The girls allege the boys followed them from the Broadmeadows train station before the attack.
The head of the Sexual Crimes Squad, Detective Inspector Glenn Davies, says the offenders may have attacked other girls in the area.
"We believe that this is a group of people who socialise together," he said.
"We believe that they congregate in the Broadmeadows and Roxburgh Park area and that they're known to people in the area.
"We believe that the family and friends and other people who know these people have the key to identifying them and those people should come forward and speak to the police about them."
Detective Inspector Davies says there may be more victims.
"We have some fairly responsible information that they are responsible for some other attacks on women in the area," he said.
Detective Inspector Davies says young women need to be concerned about their safety.
"Young women need to look out for each other and parents need to take a role in being protective of their daughters," he said.
Witnesses who were in the park where the girls were attacked have come forward with information about the assault.
Police are examining CCTV footage from Broadmeadows railway station as they try to identify the attackers.
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