Two severed left hands allegedly tie the killings of two children and a teen.
A youth gang was targeting Sudanese males to seek revenge for Kon Hsu Sein's murder when they attacked two boys, prosecutors allege.
Mr Sein, 18, died in December 2024 after a bloody brawl in Melbourne's outer west, with five people charged over his alleged murder.
About nine months later Chol Achiek, 12, and Dau Akueng, 15, were set upon by a group of males as they walked home from a basketball match in Cobblebank, in the city's outer northwest, on September 6.
Eight young men, aged 15 to 19, are charged with their murders and the youngest applied for bail at the Supreme Court on Wednesday.
Prosecutor Kristie Churchill SC said police investigators believe Chol and Dau were killed by a youth gang "specifically targeting Sudanese males" over Mr Sein's killing.
Those accused of Chol and Dau's "incredibly violent and horrific" killing did not know the two children, she alleged.
Detective Jarrad Brookman told the court one of the co-accused in the Cobblebank double murder was present when Mr Sein was killed by a youth gang of South Sudanese men.
Asked whether there were similarities between the injuries suffered by each of the victims, he said: "Yes, Kon's left hand was severed, in this situation Dau's left hand was severed".
Ms Churchill argued the motive for the murder was "retribution, revenge" as she opposed the 15-year-old boy's release on bail because he presented a risk to community safety.
"There's no evidence or no information that those tensions have abated or ceased," she said.
The families of Dau and Chol remained "terrified" and had obtained home security or relocated in the months since, she said.
Ms Churchill said the prosecution had a "very strong circumstantial case" against the teen, who cannot be named for legal reasons.
Blood found on grey tracksuit pants seized from the teen's home allegedly connected him to Dau's murder, she said.
He was also seen on CCTV getting into a car the group used, carrying a machete, and then seen getting out of the car near the attack scene, Ms Churchill said.
Prosecutors allege he conducted incriminating internet searches, cell tower evidence placed him near the offending and he caught an Uber home from one of the co-accused's homes after.
However, the teen's barrister Colin Mandy SC said his client should be bailed as conditions, including him moving to Queensland to live with his parents, would ameliorate any risks to the community.
His grandmother told the court she was willing to hand over her life savings of $100,000 as surety to secure his release.
Mr Mandy said it could take 18 months to two years for his client to face trial, because of the number of co-accused, and questioned the strength of the prosecution's evidence against him.
"The court must consider all the options before remanding a child in custody," he said.
Justice James Elliott found the teen presented an "unacceptable risk" to endangering the safety of the community if released, as he denied him bail on Wednesday afternoon.
He pointed to photos found on the boy's phone, which allegedly show him holding a machete and making gang signs.
Additionally, if he allowed the teen to move interstate there would be no bail supervision because of it being a different jurisdiction.
His mother cried in court as he was remanded into custody. The teen will return to a children's court on February 18.
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