A one-armed explosives expert belonging to Colombia’s last remaining rebel group has been blamed for a car bombing against a police academy that left 21 people dead.

Defence Minister Guillermo Botero said the man who carried out Thursday’s attack, Jose Aldemar Rojas, was a member of the National Liberation Army, or ELN, and known by his alias Mocho Kiko.

Even though Rojas had no criminal record, intelligence reports and testimony in legal cases indicate Rojas lost his arm making explosives during a long career in the ELN rebel cell near the border with Venezuela, Chief Prosecutor Nestor Martinez said.

Overnight, the death toll from the Thursday morning bombing more than doubled to 21, making it the deadliest attack in Colombia in over a decade.

It proved especially unsettling because the target, the General Santander school, is one of the most protected installations in the capital and indications it may have been the result of a suicide bombing — something unprecedented in decades of political violence in the South American nation.

President Ivan Duque, visiting the academy in the aftermath, was careful not to attribute blame to any armed group even while condemning what he called a “miserable” terrorist act that recalled some of the bloodiest chapters of Colombia’s recent past.

“The terrorists are looking to intimidate us as a society and attack the state,” Mr Duque said in a televised address in which he declared three days of mourning. “Colombia will demonstrate that it is a strong state, united and won’t break in the face of the dementia of these aggressions.”

Colombia Bombing
Family members of victims of a bombing gather outside the entrance to the General Santander police academy (John Wilson Vizcaino/AP)

Among those killed was a top-of-class female cadet from Ecuador, while two visiting students from Panama were among those injured

With the help of security cameras, authorities identified the bomber as 56-year-old Rojas, who also died in the attack.

Mr Martinez said Rojas drove a 1993 Nissan pick-up loaded with 80 kilograms of explosives past a security checkpoint and on to the school’s leafy campus, where a start-of-the-year ceremony had just finished.

There were reports that when bomb-sniffing dogs detected the explosives the driver got nervous and floored the vehicle past the barrier and on to the campus, where it exploded moments later in front of a red tile-roofed dormitory for female cadets.

Little is known about Rojas. Records show he bought the car last year and had it inspected six months ago in the eastern city of Arauca, near the border with Venezuela.

The same volatile area is a stronghold of the National Liberation Army, or ELN, the country’s last remaining rebel group following a 2016 accord between the government and the Revolutionary Armed Forces of Colombia (Farc) that saw some 7,000 rebels disarm.

Investigators are reportedly looking into Rojas’ possible ties with the rebel group after reports that he was an explosives expert for an ELN cell who went by the alias Mocho Kiko.

The ELN has been stepping up its attacks on police targets and oil infrastructure amid a stand-off with the conservative Duque government over stalled peace talks.

A year ago, the group claimed responsibility for the bombing of a police station in the coastal city of Barranquilla that left five officers dead.

But until now the Cuban-inspired group, which is believed to have around 2,000 guerrilla fighters, has never been capable or much interested in carrying out such a high-profile act of violence.

Thursday’s attack was the deadliest since a 2003 car bombing against the elite Bogota social club El Nogal that left 36 dead, an incident that hardened Colombians’ resolve against the Farc.

Mr Duque has demanded the ELN cease all attacks and kidnappings as a condition for restarting the talks and has condemned Venezuela and Cuba for allegedly providing a safe haven for rebel leaders even as their troops continue to sow violence in Colombia.