The blood was spattered on the fence, smeared in a bloodied handprint near the front door.
The "bright and airy white cottage" in Malvern East had been rented off Airbnb for a teenage house party.
But the party turned into a wild brawl on Saturday night when gatecrashers suddenly showed up - a group police are now investigating for links to a youth gang in the area.
Neighbours heard the music cut out when the gatecrashers arrived.
Someone grabbed a microphone, shouting words to the effect of: "Stop! Everybody out of the house, now!"
A huge fight then spilled out onto the street.
One neighbour's child, a 13-year-old boy, said he had been kept awake by the noisy party before witnessing the large brawl.
"They all got on to the street and they started punching on," he said.
"We saw people jumping over the back fence. They broke a couple things. My mum got so scared."
There was yelling and screaming inside the house too - and a group of youths hiding in the backyard, his father said.
"You could hear them saying, 'I'm scared. I'm scared.' They were trying to figure out how to get away without going out the front door."
Police arrived to find a crowd of about 60 people, some believed to be the gatecrashers, standing outside the Prior Road home, but the group scattered when officers arrived.
Paramedics treated at least four people at the scene, an Ambulance Victoria spokesman said.
A boy, believed to be in his late teens, was seriously hurt in the brawl, suffering a head injury and a broken finger.
He was taken to The Alfred hospital but released later on Sunday afternoon in a stable condition.
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A neighbour's brick retaining wall had been pulled down during the brawl.
Broken glass and empty plastic water bottles remained scattered outside the home the next morning.
Detective Senior Constable Paul Thomas said the party had been promoted on Facebook with partygoers paying a $10 cover charge.
About 80 people, mostly in their late teens, were inside the home when 30 to 40 people showed up in cars, he said.
It's not known if they knew anyone inside, but that's when the altercation occurred, he said.
"The organisers of the party, their money has been allegedly stolen as well," he said, adding how they have apologised to the neighbours.
Witnesses have told police the gatecrashers were African youths, although African youths also attended the house party.
Police stressed the incident is not related to the Apex gang, but it is being investigated for potential links to a different gang in the Springvale and Dandenong area.
The two-bedroom home was bought last year.
The online profile attached to the Airbnb listing is for a young woman, a university student, who says she lives with her parents and rents the property for those who love to travel.
"Melbourne is a lovely city and having lived here almost all my life I hope that others can get to love it and know it as much as I do," she wrote.
The listing was advertised for a nightly rate of $161 and clearly stated no parties or events were allowed.
The Airbnb listing's availability was taken down on Sunday while the homeowners did not respond to a request for comment.
A middle-aged man who was helping clean up at the property on Sunday morning declined to comment before saying, "I'm trying to do the right thing," and jumping in his truck and driving off.
Several young men, including a man who said he was the party's DJ, declined to comment as well when they arrived back at the house.
Police have made no arrests as the investigation continues.
Anyone with information is urged to contact Crime Stoppers at 1800 333 000 or www.crimestoppersvic.com.au.
With Cameron Houston