The protestor had a gun on him. The model and serial number matched that of a gun he purchased in 2020. The round recovered from the state trooper’s abdomen matched that gun.
Firearms forensics is, like most criminal forensics, junk science[1]: even when the basic scientific reality is aligned any particular technique, it's heavily laundered through interpretation and not subject to rigorous statistical analysis.
(In particular, bullet analysis is complete nonsense. Prior to 2005 the standard technique was lead-composition analysis, which (1) assumed that all of the suspect's bullets were the same, and (2) assumed that similarly-manufactured bullets would have similar compositions. Neither is true, which is why the Federal government no longer uses it as evidence. It's unclear whether the same is true for Georgia and the GBI.)
Edit: A more specific reference for ballistic analysis[2], which appears to be what the GBI used here.
[1]: https://en.wikipedia.org/wiki/Forensic_firearm_examination#C...
[2]: https://www.sciencedirect.com/science/article/pii/S2589871X2...
The cops traced it back to Teran and went into the protest encounter expecting to be dealing with a cop killer.
Kid had no idea what was coming; APD are thugs an environment that self-selects for them. They took no chances and wasted him.
Covering up a summary execution is way easier than conspiracy to commit it.
The family claims friendly fire. I'd believe it. Accidental discharge would explain why no GSR was found on his hands.