Ramon Cardenas, who was Estrada's political adviser, was arrested following a raid on his home in a plush village near a residential and commercial building where the mutineers had holed up before surrendering late Sunday.

Police said they seized from Cardenas' home military uniforms and other materials.

Interior Secretary Jose Lina earlier Monday said the military officers did not act on their own and had backing from political figures close to Estrada.

Evidence was also being gathered against key Estrada ally, opposition senator Gregorio Honasan, who himself in the late 1980s led several coup attempts against the government.

The 296 mutineers accused Arroyo of corruption and demanded she step down. After a 22-hour standoff with pro-government forces, however, the coup plotters surrendered and agreed to be returned to barracks.

WAR.WIRE