The savage murder and sexual assault of a 13-year-old girl in Melbourne more than 40 years ago has never been solved.

Now Victoria Police is offering a $1 million reward for information to bring the killer or killers of Denise McGregor to justice.

At 6.15pm on Monday, March 20, 1978, Denise and her 11-year-old sister walked from their Bell Street home in Pascoe Vale in the city’s north to a hamburger shop.

They arrived about 6.30pm and paid for their food with a $5 note given to them by their mother.

The girls had started to walk home when Denise handed the food to her sister and told her she was going to buy drinks from a milk bar.

Denise’s sister got home about 7pm but Denise failed to return so she went back to the milk bar to look for her.

Unable to find Denise, her sister went back home and she and her mother got in their car and searched nearby streets.

The following day, Denise’s partially clothed body was found beside Merriang Road in Wallan East.

She had been sexually assaulted and beaten to death.

Police at the time described the injuries suffered by Denise as sickening.

Detectives believe there are still people out there who know what happened to her.

Of particular interest is the fact Denise had used a CB radio on a couple of occasions at one of her girlfriend’s houses.

During these calls, she had made contact with an unidentified male with the call sign ‘Lightning One’.

Over the past 43 years, police have spoken to hundreds of people and followed up on an “enormous” number of leads, but without success.

Police say Denise was well known and popular amongst children of her age in the area and was known to frequent an amusement parlour in Broadmeadows.

“She also attended the local high school and by all accounts was a typical teenager,” police said in a statement on Wednesday.

This is not the first time a reward has been put up.

In June 1978, a $50,000 reward was offered for information about the case.