Alina Kauffman, 24, and her Ernesto Salazer, 15 (pictured together) were killed in a fatal car accident last week

Police have made fresh arrests over a car crash that killed two young siblings, with detectives taking the alleged Mercedes driver’s girlfriend and one of his passengers into custody. 

Alina Kauffman, 24, was picking up her brother Ernesto Salazer, 15, from work when they were struck by an allegedly stolen car at Heckenberg, in Sydney’s south-west, about 9.20pm on Friday.

The siblings were just metres away from their home when a Mercedes ploughed their vehicle into a stationary Toyota Rav 4, flipping their Toyota Echo into its side and killing them instantly.

The accused driver Johnson Kokozian, 20, has been hit with several charges over the accident and has been refused bail. 

Police will allege the young father was driving with a disqualified license when he hit the pair before running from the scene and leaving them to die. 

Alina Kauffman, 24, and her Ernesto Salazer, 15 (pictured together) were killed in a fatal car accident last week

Alina Kauffman, 24, and her Ernesto Salazer, 15 (pictured together) were killed in a fatal car accident last week

Alina Kauffman, 24, and her Ernesto Salazer, 15 (pictured together) were killed in a fatal car accident last week

A man was pictured arrived at a police station in the back of a patrol wagon on Wednesday

A man was pictured arrived at a police station in the back of a patrol wagon on Wednesday

Kokozian's girlfriend is pictured at court for her partner's hearing last week

Kokozian's girlfriend is pictured at court for her partner's hearing last week

Police have taken another man and a woman into custody as they continue to investigate the crash

Now, detectives have had a breakthrough on the case – with officers arresting a man who was allegedly a passenger in the Mercedes.

Footage shows the man arriving at a police station in the back of a patrol vehicle on Wednesday.

He isn’t expected to be charged over the crash, but police will allege he deliberately withheld information to protect Kokozian. 

Meanwhile, Kokozian’s girlfriend was taken into custody outside Liverpool Local Court on Wednesday, where her partner’s case was briefly mentioned.  

Kokozian did not appear on screen, but his girlfriend was there to support him – sitting in the back of court wearing a checkered coat and white stilettos.

As she left the hearing, she made it just 30 metres away from the court before a group of police approached her.

Officers led her into the nearby police station. It is understood she is being questioned in relation to the crash.

Kokozian has been charged with two counts of failing to stop and assist after vehicle impact causing death, two counts of dangerous driving occasioning death, negligent driving occasioning death, and driving a vehicle during a disqualification period. 

Police believe there were three people – including the driver – in the Mercedes at the time of the crash. 

The driver of the Toyota Echo (pictured) Alina Kauffman, 24, and her 15-year-old brother Ernesto Salazer and were treated by paramedics at the scene but were unable to be saved

The driver of the Toyota Echo (pictured) Alina Kauffman, 24, and her 15-year-old brother Ernesto Salazer and were treated by paramedics at the scene but were unable to be saved

The driver of the Toyota Echo (pictured) Alina Kauffman, 24, and her 15-year-old brother Ernesto Salazer and were treated by paramedics at the scene but were unable to be saved

Police have charged Johnson Kokozian (pictured) over the crash. The 20-year-old denies he was behind the wheel of the Mercedes

Police have charged Johnson Kokozian (pictured) over the crash. The 20-year-old denies he was behind the wheel of the Mercedes

Police have charged Johnson Kokozian (pictured) over the crash. The 20-year-old denies he was behind the wheel of the Mercedes

Mother Angelina Kauffman said earlier this week that she was appalled at the actions of the passengers of the Mercedes who allegedly left her children to die.

‘They just ran and left them, like (they’re) nothing,’ Ms Kauffman told 7News.

She also criticised those who decided to take footage of the crash with their smartphones instead of helping her children, saying ‘help, do something’.

About 150 people gathered on Sunday night to pay tribute to the brother and sister.

Mourners were seen placing cards, flowers and toys at the roadside crash site during the vigil.

Alina Kauffman, 24, was killed in Friday night's crash

Alina Kauffman, 24, was killed in Friday night's crash

Alina Kauffman, 24, was killed in Friday night’s crash

Ernesto Kauffman, 15, is pictured the family pet

Ernesto Kauffman, 15, is pictured the family pet

Ernesto Kauffman, 15, is pictured the family pet

Ms Kauffman said Alina was a dedicated nursing student with a kind heart, while Ernesto was an animal lover who was working at K-mart saving for his first car.

She explained her daughter had collected her son from his new job at Kmart and the pair were nearly home when they were hit.

‘Alina called me and said ”mum I picked up my brother, we are going to get some food and then we are coming home”,’ Ms Kauffman said.

‘I said ”are you okay” and they said ”yes mummy”.’

A vigil (pictured) was held for the brother and sister killed in a horror crash when an alleged stolen Mercedes smashed into their car just metres away from their home in Heckenberg

A vigil (pictured) was held for the brother and sister killed in a horror crash when an alleged stolen Mercedes smashed into their car just metres away from their home in Heckenberg

A vigil (pictured) was held for the brother and sister killed in a horror crash when an alleged stolen Mercedes smashed into their car just metres away from their home in Heckenberg

When she didn’t hear from them in 20 minutes, Ms Kauffman and her other child tracked their location down via social media.

The distraught mother said she arrived at the scene just minutes after the crash.

Officers arrested 20-year-old Johnson Kokozian after he handed himself into Liverpool Police Station on Saturday.

Kokozian denied that he was behind the wheel but was charged over the crash and refused bail at Parramatta Court on Sunday.

Kokozian allegedly filmed himself eating KFC in the hours before turning himself into police.

The Mercedes was reported stolen by Kokozian’s father after police attended his address about an hour after the crash.

Police are also on the hunt for the person who filmed the crash victims dying inside the car before sharing it to social media.  

A six-second video circulated online on Sunday of the moments after the crash showing the two siblings sitting inside the wreckage.

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