I was surprised when Jaime Xavier Lopez, the head of Sacred Heart, a notorious "martial-arts" group, told me to meet him at the government's Office of Cadastral Surveys and Property, where he has his day job. Or that's where he did work, since he is now imprisoned.

Lopez is well-educated, soft-spoken and unassuming, not quite what I expected from a gang boss. According to him, Sacred Heart has 6,000 members and 10,000 students enrolled in a four-year course of training.

One eye locks on me while the other wanders off as he denies that his martial-arts group has links with prominent political opposition parties.