Police have released footage of a re-enactment leading up to the moments a young mother was "brutally sexually assaulted" in Melbourne in 2013 in the hope of finding the man responsible.

The released footage comes just hours after Victoria Police announced a $500,000 reward for anyone who comes forward with information in relation to the incident.

Graphic images of the victim taken after the attack were also released by police today to show the "reality" of the crime.

The woman, named Chloe, was 22 years old when she was walking down King Street at 3am on June 30, 2013, and was approached by a man near the La Trobe Street intersection.

Police say the man then followed her from King Street to Victoria and Chetwynd Street before grabbing the woman “in a bear-hug” as they passed Browns Lane.

The attacker then dragged the 22-year-old down the lane, punching and kicking her repeatedly in the head before sexually assaulting her.

"I walked up a street and noticed a guy behind me and then walked up my street and noticed him again and then after that I just remember being hit in the side of the head," an emotional Chloe said in a recent interview with police.

"It destroyed me for a really long time. I was a new mum and couldn't be the mum that I wanted to be because I was dealing with this.

"As much as it damaged me, I think it damaged me and my son's relationship.

"You should be able to walk where you want to walk and do what you want to do. You shouldn't have to fear for your life."

Sexual Crime Squad Detective Inspector Steve Wilson spoke to the media today and described the attack as "an extreme case".

"The reason we encourage people to look at the photos is to see this is the reality of what we do and what happens," Det-Insp Wilson said.

"It sometimes can be lost as being just another incident that is often reported to us.

"Sometimes we need to bring home the true physical and mental impact. It's one of the most extreme cases we've had.

"Brutal is not a word I use very often but I think it's the best way to describe this attack. She was hit in the head initially, dragged down a lane way and from there she was continually punched and kicked by the offender and sexually assaulted."

Det-Insp Wilson says the offender is "somebody we need to get off the street".

"We've got a number of persons of interest, one in particular, but we still require the assistance of the public to provide that last piece of information that we need," he said.

"We're particularly interested in speaking to four males who Chloe may have spoken to as she walked up King Street. I want to re-emphasise these males had nothing to do with this assault. They're purely potential witnesses for us.

"We're not going to give up on this and we're not going to give up on Chloe.

"We have taken the unique step of re-enacted the whole situation through Crime Stoppers."

The man, who is described as being of Asian or Indian appearance, in his late-20s at the time, with a medium build, cropped black hair and stubble, was last seen fleeing down Chetwynd Street.