Family members have spoken of their trauma and heartbreak in losing loved ones murdered in a spate of serial killings, as police offer an unprecedented $6 million reward to find the killer.

No one has ever been charged over the “Tynong North murders” of six women in Melbourne over 16 months in the early 1980s, with the bodies of four women found in Tynong North, and the bodies of two other women found in Frankston North, in southeast Melbourne.

Police said six $1 million rewards will be offered to find the person responsible for the murders of the women, who were killed between May 1980 and November 1981 and aged between 14 and 73 years old.

Victoria Police Homicide Squad Detective Inspector Mick Hughes said police believed one of the victims, Bertha Miller, had been approached by a man at a tram who had noticed she was carrying a bible, two weeks before her death.

“She spoke to a friend after that and was pretty encouraged, she saw that as an opportunity to talk Christianity to that person,” he said.

“We’ve never identified who that is, and we’re working on the principle there’s a good chance he is our offender.

“If we look at all of the victims, they’ve either been using public transport or close to, so he’s clearly seen a way in to talk to Bertha, because everything I’m told about her, she wouldn’t engage with people unless there was a reason to do so,” he said.

Their bodies were found hidden in scrubland at Frankston, in bayside Melbourne, and at Tynong North, south-east of Melbourne, and the offender tried to hide their identities by taking their personal items.

‘Terrible damage to families’

Allison Rooke was the first of the women to fall victim to the killer and her son Keith said bringing the killer to justice would help his family to talk about his mother.

“We’ve had a traumatic time and it’s a sad way to lose our mum — a mother of six — and she was a great mum and now everyone’s had to move on, it’s a lot of time, but still we would love to see some finalisation,” he said on Saturday.

“It would also allow us within our own family, children, grandchildren, great grandchildren, to talk about it and make sure that our mum’s not remembered just for what happened, but remembered for the great person that she was,” Mr Rooke said.

Cheryl Goldsworthy was the best friend of 14-year-old victim Catherine Headland.

“It changed us all … we thought we were safe. There was a group of us and we always stuck together, basically climbing over the back fences at night because you don’t go out at night,” she said.

“It shocked me and shocked us all. It still does. It dictated how I raised my children, and I know it also had the same effect on her other friends and their daughters.

“I wouldn’t let my girls go out, I wouldn’t let them go on a bus because it was broad daylight and it just should never happened, she just had to cross a street.”

“The more that it’s brought up, and the more that it’s publicised, and the more people that know about it, sooner of later somebody’s going to say something and put it to rest for us,” she said.

Six cold case victims:

• Allison Rooke, 59, was planning to catch a bus to the shops when she was last seen leaving her Frankstown North on May 30, 1980.
Her body wad discovered weeks later in scrubland on July 5, 1980.
• 
Bertha Miller, 73, left her Glen Iris home to catch a tram to attend Wesleyan Methodist Church in Prahran on August 10, 1980.
• Catherine Headland, 14, disappeared after she left her boyfriend’s Berwick home on August 28, 1980 to catch a bus to the Fountain Gate Shopping Centre Narre Warren.
• Anne-Marie Sargent, 18, left her mother’s Cranbourne home on October 6 to catch a bus to Dandenong. 
All three women’s bodies were located after a group of men found human remains near a quarry in Tynong North on December 6, 1980.
• Narumol Stephenson, 34 was last seen outside a friend’s home in Park Street, Brunswick in the early hours of November 29, 1980. 
Her remains were located after a man changing a tyre off the Princes Freeway in Tynong North on February 3, 1983 noticed a bone sticking ouf of the bush.
• Joy Carmel Summers, 55, was last seen at a bus stop in Frankston on October 9, 1981.
Her body was later found in scrubland in Frankston North on November 22.

—with ABC/AAP