The Indonesian Islamic group Jemaah Islamiah is the only group capable of carrying out the bombings at two Jakarta hotels, according to several terrorism experts.
Bombs exploded at the city's Ritz-Carlton and Marriott hotels on Friday, killing nine people and injuring dozens.
Jemaah Islamiah (JI) has been blamed for a string of bombings on local and Western targets in Indonesia in recent years, including the 2002 Bali bombings and the 2003 attack on the Jakarta Marriott.
The Indonesian authorities arrested many of JI's leaders in the aftermath of Bali, and has since made considerable progress in tackling security threats from militant Muslims, bringing a sense of greater political stability.
There have been no major bomb blasts for several years, and this month's presidential election passed off peacefully.
Bashir still at large as 'prime motivator' of violence
But Rohan Gunaratna, head of the Singapore-based International Centre for Political Violence and Terrorism Research, says the violence in Indonesia will not stop until JI's "spiritual leader", Abu Bakir Bashir, is put behind bars.
Mr Gunaratna thinks that younger elements or a "faction" of JI may be responsible for the latest blasts, for which no one has yet claimed responsibility.
While JI is made up of splinter factions, he says, it's the only organisation capable of acts of terror like those at the Ritz-Carlton and Marriott.
He says Abu Bakir Bashir remains the movement's spiritual leader and prime motivator of violence.
'Pair of willing suicide bombers' required
The Australian Strategic Policy Institute's Carl Ungerer agrees that a small JI splinter group may be responsible; and Stratfor, a private-sector intelligence group based in the US, also fingers JI.
"Despite their setbacks and lack of activity in recent years, this type of attack takes very few resources to carry out," Stratfor says.
"Initial details indicate that the attack comprised a pair of small, improvised explosive devices (IEDs) and a pair of willing suicide bombers."
Too soon to say, says another expert
But another international terrorism expert, Jakarta-based Sidney Jones, says it's too early to arrive at any conclusions as to who's behind the blasts.
"Jemaah Islamiah has many splinter groups," Ms Jones says. "It is simply too early to comment."
