By Caroline Zielinski
A serial sex offender who has been targeting women in Melbourne's west since April has struck again.
Hobsons Bay detectives say the man has preyed on 13 women who walked or jogged on Mason Street, Newport, and in Altona North between April 29 and August 10.
In the most recent attack, on Sunday, a woman was assaulted while walking on Seventh Street, Altona North, about 7.45pm.
Detective Inspector Martin Allison said the offender, believed to be a fair-skinned man who wears a dark, hooded top pulled over his face and has ridden a mountain bike during two of his attacks, targets women between the hours of 6am and 8am, and 6pm and 8pm.
In all cases but the latest one, the attacker has grabbed his victims from behind and sexually assaulted them, the detective inspector said.
The offender approaches the victims silently and does not speak during the assault.
"And because most of the offending is done from the rear, we haven't actually got a facial description of the offender," he said.
Several women were attacked while exercising and wearing earphones, and one victim was wearing business clothes.
Detective Inspector Allison said although the attacker does not throw the victims to the ground and assault them, police were nonetheless concerned that the assaults could get worse.
"We're talking about an individual whose behaviour is leading police to be concerned about the escalating nature of that behaviour," he said.
"We don't think we're talking about a rapist ... [but] research and history tells us this type of offending ... can potentially become more sinister."
He said additional police officers have been dispatched to patrol the area, both covertly and overtly.
The detective also encouraged women to exercise with a partner to avoid being targeted.
"We want to heighten community awareness around this offending, and we'd like to encourage all woman who are exercising to do so with a companion," he said.
"We would also encourage [the women] to not wear earphones."
Any future victims were also urged to contact police immediately after the assault to increase the likelihood of the attacker being caught, Detective Inspector Allison said.
Detectives will set up an information caravan on Mason Street each evening this week in a bid to gather more information about the attacks.
In May, police revealed they were hunting a man who had indecently assaulted four female joggers in Newport and Yarraville between 6am and 8am.
The victims were all aged between 20 and 30 years.
The attacker was described as fair-skinned, aged between 20 and 30, and about 160 centimetres tall.
A police spokeswoman said detectives were investigating whether the two cases were linked.
Police are asking anyone who has noticed a man lurking in the areas during early morning and evening to contact Crime Stoppers on 1800 333 000.