(BOGOTA, Colombia) — Colombian authorities said that a one-armed explosives expert belonging to the country’s last remaining rebel group carried out a car bombing against a police academy that left 21 dead and more than 70 wounded. Chief Prosecutor Nestor Martinez said at a press conference Friday that the man who carried out Thursday’s brazen attack, the deadliest in 15 years, was a longtime member of the National Liberation Army, or ELN. Even though Jose Aldemar Rojas had no criminal record, intelligence reports indicate that the 56-year-old man also known by the alias Mocho Kiko lost his arm manipulating explosives during his long career as an operative in an ELN rebel cell near the border with Venezuela, Martinez said. Thursday’s attack recalled some of the bloodiest chapters of Colombia’s recent past and has raised tough questions about lingering security threats in the wake of a 2016 peace deal with FARC rebels.