Analysts at the Brussels-based International Crisis Group (ICG) said the group led by Malaysian Islamist Noordin Mohammed Top was finding it "disturbingly easy" to recruit members to carry out fresh attacks.
"More than a month after the 17 July, 2009 hotel bombings in Jakarta, Noordin Mohammed Top remains at large, but his network is proving to be larger and more sophisticated than previously thought," the ICG said in a report.
"Noordin may still be the commander, but he has some exceedingly well-connected lieutenants who made their debut in the hotel bombings."
The twin suicide blasts at the JW Marriott and Ritz-Carlton hotels killed nine people including two bombers and six foreigners. They marked the bloody end of a four-year hiatus in such attacks in the mainly Muslim country.
Noordin, 41, is the most wanted extremist in Indonesia and calls his group "Al-Qaeda in the Malay Archipelago".
He allegedly received Al-Qaeda backing for an attack on the Marriott in 2003 which killed 12 people.
Police say five cell members, including the two bombers, have been killed and five arrested, including an Indonesian publisher known on the Internet as the "Prince of Jihad" who helped arrange funds for the attacks.
Counter-terror squad officers arrested the publisher, Mohammed Jibril Abdurahman, 24, near Jakarta late Tuesday and raided the office of his Ar-Rahmah media company.
Police believe the Pakistan-educated suspect was an accomplice of a Saudi national who was arrested in Indonesia earlier this month on suspicion of smuggling money from abroad to pay for the July 17 operation.
The source of the funds is not known, but police have said they are investigating whether the money came from Al-Qaeda brokers in the Middle East or South Asia, among other possible donors.
ICG analyst Sidney Jones said Mohammed Jibril was not a known member of Al-Qaeda, but had reportedly had contacts with Osama bin Laden's group during his years studying Islam in Karachi, southern Pakistan.
He is believed to have joined a group in Pakistan known as Al-Ghuraba, or The Foreigners, which trained Southeast Asian members of the Jemaah Islamiyah (JI) regional terror network blamed for the 2002 Bali bombings that killed 202 people.
Al-Ghuraba was set up in 1999 by Hambali, the Indonesian alleged point-man for Al-Qaeda in Southeast Asia who is in US custody at Guantanamo Bay, analysts said.
The August 2003 arrest of Hambali, seen as JI's operations chief, led to the breakup of Al-Ghuraba but the ICG said the Pakistan connection could have been re-established.
Hambali's younger brother and Al-Ghuraba alumni Gun Gun Rusman Gunawan was sentenced to four years' jail in Indonesia in 2004 for helping to finance the 2003 Marriott attack. He served only two years and is now free.
"Do you think Al-Ghuraba is a terrorist movement?" Mohammed Jibril's family spokesman Irfan S. Awwas told reporters when asked if the publisher and Internet blogger was a member of the group.
"As a student there (in Pakistan), anyone can join any organisation such as Al-Ghuraba -- it's not forbidden."
Ar-Rahmah has pioneered the sale of video discs from Al-Qaeda and other Islamist groups in Indonesia, the ICG said.
Last year it launched the glossy Jihadmagz magazine, which glorifies global terror attacks.
Mohammed Jibril's father, radical cleric Abu Jibril, visited police headquarters to demand his son's immediate release.
Source: AFP Asian Edition