SEMPORNA - The father was a notorious pirate before his death in the late 1990s.
Muktadir, a Filipino, terrorised the Sulu and Celebes seas separating Sabah and the southern Philippines.
His five sons, known as the "Muktadir brothers", are part of a well-armed family of kidnappers.
Malaysian security forces are hunting them down as they believe the brothers are behind the last four cross-border kidnappings in the east coast of Sabah since November.
Sabah CID chief Sr Asst Comm Omar Mammah said the police believed the same group was involved in all four abductions over the past seven months. However, he did not disclose the identity of the kidnap-for-ransom (KFR) group.
According to intelligence officers interviewed by Sunday Star, the Muktadir brothers are one of the most active of the 14 known KFR groups in the southern Philippines.
Unlike the Muktadir brothers, the other KFR groups operate within the Philippine waters.
Malaysian security forces have identified three of the brothers as Nelson, Badung and Gadafi, while two others are reportedly going by the name Murphy Ambang Ladia @ Gulam and Ali, who is also known as Braun.
The brothers are believed to be based in a water village in Sitangkai island in the Tawi Tawi chain of islands that straddles Sabah's east coast.
They used to live in Semporna, Sabah, when their father worked as a security guard in the district before he became a notorious pirate operating in Semporna waters from the southern Philippines.
Intelligence sources said Nelson was a former Moro National Liberation Front (MNLF) member.
He lived with his wife and child in Kampung Bangau Bangau in Semporna and worked as a carpenter and moneychanger while trafficking in syabu.
The brothers established crucial local links through relatives and friends who helped them whenever they carried out a kidnapping.
They were also familiar with the surrounding sea and the security forces' movements.
Closely-linked with cross-border smugglers, the brothers own numerous speed boats and a cache of weapons that make them a feared clan in the southern Philippines.
The brothers, according to Filipino smuggler sources who regularly ply the route between Sabah and Tawi Tawi, bought their 40HP boats in Tawau and used them in the abductions.
The sources also believe that the Muktadir brothers smuggled weapons - M16 and Garand rifles, M203 grenade launcher and pistols - from the southern Philippines and hid them in uninhabi-ted islands in the east coast of Sabah.
They sneaked into Sabah as Filipino immigrants and blended in with the large Malaysian-Filipino community living in water villages.