MEXICO CITY (Reuters) - Mexican police arrested a top lieutenant of the Zetas drug cartel who was linked to the murder of a US immigration agent in February, Mexico's security ministry said on Monday. Police captured Jesus "El Mamito" Rejon in a Mexico City suburb on Sunday," the ministry said in a statement. Rejon is a founding member and currently third in command of the Zetas, which was started by former Mexican special forces soldiers and is considered the country's most brutal cartel. Turf wars between the Zetas and other cartels have transformed parts of Mexico into lawless killing grounds and scared away some foreign investors.