The article you sent machine translates into just Google Pixel, I see no mention of "6a" anywhere. This other article also has the same: https://www.gva.be/cnt/dmf20230711_95537678
Are you sure it is a Pixel 6a?
Pixel 6a or not, all you can really do is speculate. There could be many ways, such as:
- The suspect was stupid.
- The suspect surrendered the information.
- The police got access at a time where he was caught and unable to perform a security mechanism.
- The unlock method was weak, or the PIN/Pattern was found through other means such as CCTV.
- (Unlikely) An exploit was used that allowed extraction.
- (If a Pixel 4 or lower) the unlock method could have been brute forced.
The mobile forensics suite Cellebrite can brute-force the PIN for the Pixel 4 and lower if the phone was unlocked once before and you are using the Advanced Services programme, allowing for a filesystem extraction:
https://web.archive.org/web/20230608135947/https://cellebrite.com/en/cas-supported-devices/
(A web archive is used as Cellebrite often blocks VPNs on their site).
It is worth noting the Department of Homeland Security did a public test result for Cellebrite on a Pixel around this time last year with a Pixel 2 and could only perform logical extraction (the weakest form of extraction where no exploitation is possible, meaning the unlock method needs to be surrendered or known beforehand): https://www.dhs.gov/sites/default/files/2022-09/22_0901_st_test_results_for_mobile_device_acquisition_tool_Cellebrite_inspector_v10.5.pdf - although it didn't go into their brute-force functionality, could be possible they weren't using Advanced Services for this test.
Mobile forensic investigator tools such as Cellebrite or Grayshift have never made an official statement for unlocking on any Tensor Pixel device in any capacity, only that they 'support' them, but not the circumstances in how they support the devices. On current plans they are all consent-required and are unable to get info on even the applications without an investigator navigating them manually (which is an extremely risky last resort move that often ends up with the evidence being inadmissable in court). If they can do exploitation then it is being withheld and quite tightly, me saying this is not an admission that they have one, you can only speculate.