BUENOS AIRES, Argentina (AP) — Police in Argentina have arrested four men suspected in the killing of a British tourist who was shot during a robbery attempt, authorities said Monday.

Authorities were searching for a fifth person, the alleged ringleader of the group that killed Briton Matthew Charles Gibbard in Buenos Aires on Saturday, according to Argentine officials.

Gibbard, 50, was shot as he and his stepson approached a luxury hotel in the Puerto Madero area of the Argentine capital. The stepson, a 28-year-old Briton, suffered a gunshot wound. The assailants were on a motorcycle and supported by accomplices in a car, and the tourists tried to resist the attack, according to an official account.

Authorities identified the vehicles used by the attackers from security camera footage and conducted more than a dozen searches in the Buenos Aires area, said Marcelo D'Alessandro, justice and security director in Buenos Aires.

Eduardo Scarzello, a senior security official, said the gang involved in Gibbard's death had operated at the city's international airport, identifying U.S., European and other tourists and following them to their destinations in order to rob them.