Two prisoners at a Tarragona jail exploited the confusion caused by the suicide of a fellow inmate on Monday morning to make their escape.
One of the fugitives has already been recaptured by the Mossos d'Esquadra Catalan regional police, while the other remains at large.
A third prisoner had also tried to escape but was apprehended by a Mossos officer.
The inmates put their escape plan into action at 9.30am when a fourth prisoner who was exercising in the prison yard said he was suffering from back pain and was taken to the infirmary, according to the regional government's director general for prison services, Xavier Martorell. It was there the inmate took his own life by tying his shoelaces around his neck and hanging himself.
The three prisoners, all from the same cellblock, made the most of the ensuing commotion to climb up to a watchtower. Martorell explained that the escapes occurred because a prison warden failed to follow emergency procedures. "One of our wardens saw a foot sticking out [from the tower], but did not activate the security protocol," he said.
Despite the fact that several inmates were all staring up at the scene, the warden paid no heed to the incident and it was not until between five and 15 minutes later that he mentioned it to another guard.
By then the three fugitives had already climbed on to the roof and got over the prison security perimeter, where they encountered a Mossos officer who succeeded in detaining one of them.
Martorell did not want to reveal the names of the escaped prisoners, though, according to the Catalan regional government, one is a Spaniard while the other is a Venezuelan national. Both were serving sentences for robbery.
This is the second jail escape in Catalonia within a week. Last Wednesday a Pakistani inmate escaped from the Modelo prison in Barcelona by swapping clothes with his visiting brother.