PIEDRAS NEGRAS, Coahuila — Gunmen assassinated the former mayor of the border city of Piedras Negras as he left a political debate.

The shooting took place shortly after 9:45 p.m. outside of the Coahuila State University Auditorium when a bearded gunman wearing gray clothing walked up to former mayor Fernando Puron Johnston and shot him once in the back of the head. The gunman then appears to shoot him twice in the chest area before running away.

A surveillance video leaked to Breitbart Texas revealed the moment when the gunman walks behind Puron and fires a handgun.

State and federal authorities carried out a large manhunt in an attempt to locate the gunman and other accomplices who may have helped him. As of press time, no arrests had been made. Emergency medical personnel rushed Puron to a local hospital where he later died from his injuries.

Puron, a candidate for Mexico’s Revolutionary Institutional Party (PRI) for a federal congressional seat, had just finished a heated political debate with candidates from other parties. Before becoming a congressional candidate, Puron had served as mayor of Piedras Negras and is credited with promoting economic growth as well as taking a hard line on seedy bars and closing down brothels and cantinas that in the past had been used as fronts by organized crime in the border city.

Ildefonso Ortiz is an award-winning journalist with Breitbart Texas. He co-founded the Cartel Chronicles project with Brandon Darby and Stephen K. Bannon. You can follow him on Twitter and on Facebook. He can be contacted at Iortiz@breitbart.com.

Brandon Darby is managing director and editor-in-chief of Breitbart Texas. He co-founded the Cartel Chronicles project with Ildefonso Ortiz and Stephen K. Bannon. Follow him on Twitter and Facebook. He can be contacted at bdarby@breitbart.com.

“J.M. Martinez” from the Cartel Chronicles Project contributed to this report.