Washington law also prohibits their possession. Prosecutors charged Niko-Semo with unlawful possession of a firearm and unlawful possession of a bump-fire stock in that case. Meanwhile, police say the 15-year-old arrested at the scene was carrying a Polymer80 “ghost gun,” an unserialized handgun assembled from parts that cannot be traced through traditional firearm records. According to court records, Niko-Semo’s criminal history extends beyond the 2024 firearms case. However, those earlier juvenile records have been sealed, preventing the public from viewing the details of the allegations.