Authorities say a weapon recently used to kill a U.S. agent in Mexico was bought by a Texas man under surveillance since last fall over suspected gun trafficking for a violent Mexican drug cartel.

Federal complaints filed against three Dallas-area men were released Tuesday, when a federal judge delayed their hearing at the request of defense attorneys. The suspects will appear in court in Dallas on Friday.

Authorities say the three suspects met in November with an undercover agent who was to take the guns to Laredo, Texas. Law officers seized the 40 weapons before they crossed the border, but authorities later learned another gun purchased in October by one of the Texas men was used in the fatal Feb. 15 attack on a U.S. Immigration and Customs Enforcement agent.