MEXICO CITY — The bodies of three tourists found in a well in Mexico's northwest all had bullet wounds to the heads, authorities say.

Australian brothers Jake and Callum Robinson, 30 and 33, and their American friend Jack Carter Rhoad, 30, disappeared on 27 April while on a surfing trip in Ensenada.

Relatives of the three men identified their bodies on Sunday after traveling to Mexico to assist authorities, a state prosecutor said.

Officials believe the men were attacked as they were trying to fend off an attempted theft of their pickup truck.

The attackers wanted the vehicle for its tires and shot the tourists when they resisted, Baja California state prosecutor Maria Andrade suggested.

Their bodies were found in a 4m (15ft) deep well about 6km (4 miles) from the site of the attack in the town of Santo Tomás on Friday.

Abandoned tents, a burnt white pickup truck and a phone linked to the missing surfers were found nearby.

A fourth body was found in the well but had been there longer and was unconnected to the case, officials said.

Two men and a woman have been detained on suspicion of direct or indirect involvement in the attack. One man has been charged with "forced disappearance".

Earlier, the FBI said it was looking into the case and was in touch with international partners.

Baja California is one of Mexico’s most violent states, as local drug gangs fight turf wars.

But the Ensenada area, about 120km (75 miles) south of the US-Mexico border and known for its surfing conditions, is considered safer and has long attracted tourists from California.

The killings have sparked fear and anger in the popular holiday spot.

Scores of protesters marched through the city on Sunday, carrying surfboards plastered with slogans written in Spanish.

“They only wanted to surf - we demand safe beaches," one said. "Australia we are with you," another said.

A group of surfers later performed a “paddle-out” ceremony, an ocean vigil to honor the trio.

Australian Treasurer Jim Chalmers said the country was thinking of the Robinson family.

"It has been an absolutely horrendous, absolutely horrific ordeal and our thoughts are with all of them today,” he said at a news conference on Monday. — BBC