Influencer Babi Cardoso was executed by gunfire on the night she disappeared, the police said as they called a halt to the search.
The 23-year-old last spoke to her mother to say she was on her way home at about 10pm on 6 September.
The influencer, full name Gabriela Evaldt Cardoso, never arrived.
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A friend heard from her around 11pm.
Gabriela, who had 38,000 Instagram followers and also worked as an app driver, had borrowed her mother’s white Volkswagen Golf.
CCTV last showed her behind the wheel at about 9pm.
Ten days later, the car turned up without number plates at an abandoned house after an anonymous tip.
Stickers had been stripped from the rear window and one hubcap was missing.
Police recovered her phone and sent a fingernail found in the car for DNA testing.
Investigators said they have a “technical conviction” she was murdered on the night of her disappearance in Tramandaí on Brazil’s southern coast.
Police chief Alexandre Souza said: “We are absolutely certain she was executed by gunshots.”
Officers found spent rounds in one search area.
“They may be the ones that killed Gabriela – or they may not be,” Souza added.
Gabriela’s mother, Rosane Maria Matos Evaldt, said she is in “inexplicable pain”.
Teams are now using metal detectors to hunt for more ammunition.
Police said they already know the motive but will not reveal it or name any suspects so the inquiry is not compromised.
Ground searches in the first zone have been halted after weeks of sweeps found no body.
Heavy rain also forced a pause on drones and sniffer dogs, as reported by Need To Know.
Officers said they may reopen a new perimeter once phone data, social media records and forensic results come back.
Police insist the investigation continues despite the original search grid being stood down.
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