SPANISH POLICE have arrested a chemistry student suspected of planning a gas attack against protesters opposed to a visit by Pope Benedict XVI.

The pontiff is due to arrive tomorrow for a four-day visit to celebrate the Catholic Church’s World Youth Day, and a protest march is scheduled for this evening in Madrid.

A police official said the suspect arrested in Madrid yesterday is a 24-year-old Mexican student specialising in organic chemistry. She would not give his name, or say whether investigators believe the man was actually capable of carrying out a gas attack.

Police said in a statement released last night that officers who searched the suspect’s apartment in a wealthy district of Madrid seized an external hard-drive and two notebooks with chemical equations that they say had nothing to do with his studies.

It said he tried to recruit people via the internet to help him, and that a computer allegedly used for this purpose was among objects seized by police.

The statement said the man had planned to attack anti-Pope protesters with “suffocating gases” and other chemicals. But it did not mention police having confiscated chemicals that could be used in an attack.

The police official spoke on condition of anonymity in line with police rules.

The statement said the suspect was in Madrid studying with Spain’s top government research body, the Spanish National Research Council and his office there was searched. The council confirmed the arrest but gave no immediate details on the Mexican.

Church organisers say the papal visit is costing about €50 million to stage. Protesters complain the government is essentially spending taxpayer’s money on the visit by granting tax breaks to corporate sponsors and perks such as discount subway and bus tickets for pilgrims.

Officials at the Mexican Embassy in Madrid did not immediately respond to telephone and email messages seeking comment.