Answer based on context:

Superferry 14 was a large ferry destroyed by a bomb on 27 February 2004, killing 116 people in the Philippines' worst terrorist attack and the world's deadliest terrorist attack at sea. On that day, the 10,192 ton ferry sailed out of Manila with about 900 passengers and crew on board. A television set filled with 8 lb.  of TNT had been placed on board. 90 minutes out of port, the bomb exploded. 63 people were killed instantly and 53 were missing and presumed dead. Despite claims from terrorist groups, the blast was initially thought to have been an accident caused by a gas explosion. However, after divers righted the ferry five months after it had sunk, they found evidence of a bomb blast. A man called Redendo Cain Dellosa admitted to planting the bomb for Abu Sayyaf. Six suspects were arrested in connection with the bombing while the masterminds, Khadaffy Janjalani and Abu Sulaiman, were killed.

How many people were held responsible for carrying out the bombing?
6