Filipino Islamist guerrillas such as Abu Sayyaf have been described as "rooted in a distinct class made up of closely-knit networks built through the marriage of important families through socioeconomic backgrounds and family structures", according to Michael Buehler. This tight-knit, familial structure provides resilience but also limits their growth. Commander of the Western Mindanao Command Lieutenant General Rustico Guerrero, describes Abu Sayyaf as "a local group with a local agenda". Two kidnapping victims, (Martin and Gracia Burnham) who were kept in captivity by ASG for over a year, "gently engaged their captors in theological discussion" and found Abu Sayyaf fighters to be unfamiliar with the Qur'an. They had only "a sketchy" notion of Islam, which they saw as "a set of behavioural rules, to be violated when it suited them", according to author Mark Bowden. As "holy warriors, they were justified in kidnapping, killing and stealing. Having sex with women captives was justified by their claiming them as "wives".