A $1 million reward is being offered as police try again to solve the murder of an 18-year-old man shot at a popular spot for young couples in Melbourne 40 years ago.
Thomas Cooper and his 16-year-old girlfriend were sitting in his Holden HQ sedan at Ricketts Point in Beaumaris on the night of August 18, 1980.
A man wearing a hat approached the car and smashed the driver's side window.
Thomas tried to drive away but the man shot him a number of times.
His girlfriend was able to steer the car away from the area and was not injured.
The unnamed girlfriend died in May this year, Victoria Police revealed on Tuesday.
The area was a well known spot for couples to go parking and Thomas and his girlfriend went there several times a week.
Homicide Squad boss Detective Inspector Dean Thomas said while the reason for the murder was unclear, Thomas's girlfriend could have been the target.
"There are a number of possibilities, including that the shooting was sexually motivated and the girl in the car may have been the target," he said.
"We know that many couples regularly went to this location so the offender may have been stalking the area."
Det Insp Thomas added police had exhausted all their inquiries.
"We've spoken to a large number of people through the course of this inquiry, all with varying motives, but at this stage we can't land on one," he said.
But he added police are confident the reward will lead to a breakthrough.
"We know what happens over time - relationships break down, relationship change and people move on," he said.
There was nothing in the backgrounds of Cooper or his girlfriend that explained the murder, Det Insp Thomas said.
He said not having the murder solved had taken its toll on his girlfriend and family.
"How do you hold up when you've lost a loved one in such tragic circumstances and you never get an answer as to why?" he said.
"It might just provide them (Cooper's family) with something."
Police have a digital composite image of a man they want to speak to that was created after Thomas' murder.
The image has been updated to show what this man might look like in 2020 and versions depict him with and without a hat.
"We're hopeful that after four decades, this person is ready to come forward and assist us and bring (Cooper's) family some justice," Det Insp Thomas said.
The $1 million reward has been increased from $50,000 and will be paid for information leading to the conviction of the person responsible.