The ghost gun allegedly in Luigi Mangione's possession when he was arrested has been matched to three shell casings recovered at the crime scene in New York.

Brian Thompson was laid to rest at a private funeral service in his Minnesota hometown on Monday. That same day, Luigi Mangione was arrested in Pennsylvania and charged with murder in connection to the UnitedHealthcare CEO’s death.

Here's what we know about UnitedHealthcare CEO Brian Thompson, who was shot to death in Manhattan on Wednesday, Dec. 4.