More than six months after Filipino and foreign fighters claiming allegiance to the Islamic State stormed this lakeside city, setting off a months-long war with US-backed Philippine troops, liberated Marawi lies in ruins and its people seethe.

Experts are still trying to understand the force they assembled, particularly the precise nature of their links to the Islamic State, said Shashi Jayakumar, who heads the Center for Excellence in National Security at Singapore’s S. Rajaratnam School of International Studies.

Philippine groups have a long history of claiming allegiance to foreign forces in a bid to gain credibility through what Jayakumar called the “veneer of jihadism.” Whatever its ties, the Hapilon and Maute group was formidable. “This was a significant force, with significant preparation. It hit everyone by surprise,” Jayakumar said.