Stop Illegal Trafficking in Firearms Act of 2021 This bill establishes a federal statutory framework to prohibit straw purchasing of firearms, trafficking in firearms, and related conduct. A violator is subject to criminal and civil penalties, including the seizure and forfeiture of the firearms and ammunition involved in the offense, property constituting or derived from proceeds from the offense, and property used to commit or facilitate the offense. The bill authorizes law enforcement to investigate straw purchasing and trafficking in firearms offenses using wiretaps (i.e., authorized interceptions of wire, electronic, or oral communications) and makes the offenses predicate offenses (i.e., underlying offenses) for prosecutions under the federal money laundering statute and the federal racketeering statute.