Mr Abdillah's has been adjourned until next week
The trial has begun of a man alleged to have assisted in the twin suicide hotel bomb attacks in Jakarta in July 2009 that killed seven people.
Amir Abdillah, 34, is charged under anti-terror laws of concealing information and harbouring terrorists.
Prosecutors said he had been the driver for alleged terrorist Noordin Top, who was shot by police in a September raid on a central Java village.
The hotel bombings ended a four-year lull in terrorism in Indonesia.
The July attacks at the JW Marriott and Ritz Carlton hotels also injured more than 50 people.
Mr Abdillah, who appeared in South Jakarta District Court on Wednesday, was arrested a month after the attacks as the first suspect in the case.
If convicted, he could be sentenced to death.
He joked with journalists and smiled during the hearing, the French AFP news agency reported.
Asked outside the court whether he regretted his actions, he thought for a few seconds and replied: "Yes," AFP said.
In court, chief prosecutor Totok Bambang alleged that Mr Abdillah had helped plan the hotel bombings and had been part of a plot to assassinate Indonesian President Susilo Bambang Yudhoyono.
Mr Abdillah is believed to have given information that led to the arrests of several other suspected terrorists, and two deadly raids in Central Java that killed four suspects.
The BBC's Karishma Vaswani says he is also believed to be the man who booked the room - number 1808 - in the JW Marriott where the bombs went off.
Police have killed six suspects and arrested more than a dozen others, including a Saudi citizen who is accused of helping to finance the bombings.
Malaysian-born Noordin Top was blamed for a string of terrorist attacks in Indonesia that killed more than 250 people.
Dec 2000 - Church bombings kill 19
Oct 2002 - Bali attacks kill 202
Dec 2002 - Sulawesi McDonald's blast kills three
Aug 2003 - Jakarta Marriott Hotel bomb kills 12
Sept 2004 - Bomb outside Australian embassy in Jakarta
Sept 2005: Suicide attacks in Bali leave 23 dead, including bombers
Indonesia suffered a number of bomb attacks - mainly linked to the militant group Jemaah Islamiah - in the first years of the century.
The country of 240 million people has been praised in recent years for maintaining a pluralist democracy, while punishing Islamists behind a series of bombings.
Attacks on two nightclubs in Bali in October 2002 killed 202 people, most of them Australian.
The Marriott Hotel was the target of a bomb attack in August 2003 in which 12 people were killed.
Since then, a combination of new laws, anti-terror training, international co-operation and reintegration measures have kept Indonesia peaceful, analysts have said.