Madrid (CNN) -- A man arrested in Madrid on suspicion of planning an attack against a demonstration to protest the visit of Pope Benedict XVI was a volunteer for the papal visit's organizing committee, a committee senior spokesman said Wednesday.
The suspect was arrested on Tuesday at the IFEMA fairgrounds by plainclothes police officers as he was about to receive a backpack and a green shirt worn by volunteers, said the spokesman, Rafa Rubio, the communications director for World Youth Day, told CNN.
A police statement Tuesday said a man studying chemistry in Madrid was arrested on suspicion he was planning an attack against a march set to protest the high cost of the visit of the pope to the Spanish capital starting Thursday, the police said.
The suspect "planned to attack using noxious gases and other chemical substances," the national police said in a statement.
The alleged target was a protest march set for Wednesday evening in Madrid, on the eve of the pope's four-day visit.
The pope arrived in Madrid on Thursday as protests took place in the city over the cost of his visit.
A police spokeswoman on Wednesday said the suspect is a Mexican national.
The police statement said the suspect was studying general organic chemistry at Spain's government-backed Higher Council for Scientific Investigations.
Rubio said the suspect, age 24, had completed the process to become a volunteer for World Youth Day and he added that the arresting officers at the volunteer check-in area were so discreet that many in the World Youth Day organization were not aware of what had happened until hours later.
The man is no longer a volunteer, Rubio said.
"His apparent thinking is not in the spirit of Christianity," Rubio said. "World Youth Day rejects all violence."
World Youth Day has 30,000 volunteers, many of them from outside of Spain.
At the suspect's home in the upscale Salamanca neighborhood of the capital, police seized a laptop computer, a portable memory device and two notebooks with notes about chemical procedures which were not related to his official studies, the statement said.
The suspect also allegedly was trying to recruit adherents through the Internet. The police statement said citizen collaboration helped lead police to the man.
The cost of the pope's visit to Spain, suffering a deep economic crisis with nearly 21% unemployment, has been top news here in recent days.
Benedict XVI is coming to World Youth Day, a weeklong series of religious events that the Roman Catholic Church organizes internationally every three years, last held in Sydney, Australia.
Organizers expect at least a million youth for the event and Madrid's streets already are filled with many thousands of young Catholics from around the globe, carrying their national flags.
Organizers say the $70 million cost is totally paid by the young people and corporate sponsors -- with no cost to the taxpayer. But others in Spain say there are substantial hidden public costs, including the 10,000 police officers on duty for security, the use of the Cuatro Vientos military air base for Mass, and a discount for visiting Catholic youth on the city's metro, at the same time as regular metro fares have risen sharply.
Critics including Spanish groups called Christian Networks, Lay Europe and a third run by atheists convened a protest march over the costs on Wednesday, and they said they expect up to 10,000 people.