The bombing of the Marriott Hotel in Jakarta came in a tense week of high-profile court cases in the Indonesian capital, raising suspicions the blast was related.
Likely to head the list of suspects is Jemaah Islamiah, the shadowy group blamed by the Indonesian Government for the 2002 Bali bombing.
Several of its members are on trial in Bali for the attack, and the verdict against one of the key suspects, Amrozi, is due on Thursday. He may face the death penalty if found guilty.
The court case of the group's alleged spiritual leader, Muslim cleric Abu Bakar Ba'asyir, is also continuing in Jakarta.
Abu Bakar Ba'asyir is charged with plotting to overthrow the Jakarta Government and involvement in church bombings in 2000, though he is not charged in connection with the Bali attacks.
Jemaah Islamiah (JI), which wants to set up a Muslim state across much of South East Asia, has been damaged by the arrest of more than 30 of its alleged members in the wake of the Bali attacks.
But security analysts have said the group remains a real threat, especially in Indonesia.
The man believed to be one of its top leaders, Riduan Isamuddin, also known as Hambali, remains at large.
Hambali is believed to be JI's link-man with Osama Bin Laden's al-Qaeda network, though he is now thought to be too high-profile a figure to be involved in either group's day-to-day activities.
Another JI member, Fathur Rohman al-Ghozi, escaped from jail in the Philippines last month.
Governments in the region have expressed concern that Al-Ghozi, an Indonesian and expert bomb-maker, could slip back to Indonesia and go into hiding in the vast archipelago.
The choice of the Marriott Hotel as a target - a well-known meeting point for Western businessmen near to several foreign embassies - would also fit JI's pattern of action.
At a planning meeting which led to the Bali attack, JI is thought to have agreed to go after low level targets - like night clubs and other places where foreigners congregated - rather than higher-profile buildings like embassies.
Until someone claims responsibility for the blast, the Indonesian police and public will have several other suspects on their lists.
Since the fall of former dictator Suharto in 1998, the country has been hit by several outbreaks of regional and religious instability.
And with presidential elections due to be held next year, rumours and conspiracy theories abound.
Within hours of the Jakarta blast, the verdict in another prominent court case was handed down.
A special human rights court sentenced Major-General Adam Damiri to three years in jail for failing to stop violence surrounding East Timor's 1999 vote for independence from Indonesia.
Indonesian authorities have warned in the past of serious dissatisfaction within some sections of the armed forces, that the trials of Major-General Damiri and 17 other Indonesian soldiers and officials went ahead.
The Indonesian Government is likely to shift the focus to another troublesome province, Aceh, which has been under martial law since May.
Indonesian troops are fighting Free Aceh Movement (Gam) rebels who want independence from Jakarta.
Police blamed Gam for a 27 April bomb blast on a Kentucky Fried Chicken fast-food outlet at Sukarno-Hartta International Airport.
Gam denied any part in the attack, which left several people injured.