Los Chapitos built their own weapons in clandestine workshops, copying the weapons and explosives they trafficked illegally from the United States. They had a network operating in Tucson and Nogales, based in Sinaloa. This was reported by the Attorney General's Office (FGR) in Mexico.

According to the Specialized Prosecutor's Office for Organized Crime (FEMDO), Los Chapitos, a faction of the Sinaloa Cartel, were in charge of the illegal trafficking of such explosives as grenades and grenade launchers, high-caliber weapons and cartridges.

The criminal organization was in charge of disassembling war objects to copy their components and manufacture them in clandestine workshops. The manufactured weapons were then "delivered in large numbers to hitmen for the criminal organization," as indicated in a news report published by the newspaper La Jornada. The FEMDO established that, at least since 2018, Martín León Romero led the arms trafficking group based in Nogales, Sonora. He had the collaboration of U.S. citizens, and even Mexican boxer Julio César Chávez Jr. may have been involved. La Jornada reported that the criminal cell had members dedicated to recruiting more people to buy firearms in Tucson. Their modus operandi consisted of "several members of the organization contacting others in exchange for money, asking them to use their credit cards and provide their addresses so that they could receive purchase orders for firearms and cartridges made online and be delivered to those addresses in the United States, and from there they were picked up by members of the criminal organization led by León Romero."

According to the cited media, it was León Romero himself who received the weapons, checked their quality and repackaged them to send them by land to Culiacan, Sinaloa, delivering them to Iván Archivaldo and other members of the Sinaloa Cartel.

44-millimeter caliber grenades and M203 model 40-millimeter caliber grenade launchers were detected among the items acquired in the United States. Also seized during U.S. investigations were 97,000 cartridges and 19 firearms.

Leon Romero was arrested in December 2024 and linked to criminal proceedings by a judge based in Hermosillo, Sonora. According to Univision, an arrest warrant has also been issued for 13 people, including Julio Cesar Jr., all allegedly linked to these illicit operations.

Chavez Jr. was arrested in early July and is also under investigation for his alleged operation as a "score settler" for the Sinaloa Cartel, particularly the Los Chapitos faction.