Olivia Burgos is accused of lying during the purchase of the gun in 2024, that would later be used to kill Chicago police officer John Bartholomew and wound a second officer.
Burgos told investigators she bought the gun in Merrillville, Indiana, for her boyfriend at the time.
Her boyfriend is not identified in the criminal complaint, but prosecutors said she told them he was a convicted felon and he gave her the money to buy the weapon.
Burgos also told federal investigators she's addicted to fentanyl and was on the drug when she bought the weapon, despite stating otherwise on a form to purchase the gun.
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It's still unclear how the suspect, Alphanso Talley, ended up with the gun, or how he got it inside Swedish hospital Saturday.
Sources tell ABC7, Talley was likely searched three times without a weapon being detected. They said they believe Talley may have hid the gun in his body.
Talley is due back in court Thursday in connection with the shooting that killed Officer Bartholomew and seriously injured his partner, who's still in the hospital.
As for Burgos, her court hearing is scheduled for Wednesday afternoon in Hammond.
Similar charges were also filed after the murder of Chicago police officer Ella French, as well.