Police are investigating e-mail messages allegedly from two groups in India that have claimed responsibility for the attack.
The explosives were in a briefcase left in a reception area filled with people attending the court not far from Parliament and the office of Prime Minister Manmohan Singh.
The blast killed 13 people and wounded 76 others.
One of the groups under investigation is the Indian Mujahedin but which police believe hasn't been active in India for a while.
The other group is the Harkat-ul Jihad al-Islami, sometimes called Huji. It's believed to have started in Pakistan and to have had links with al-Qaida.
An e-mail reportedly sent by Huji was traced to an Internet cafe in Kashmir where police detained five people.
"We can no longer point to cross-border terrorism as a source of terror attacks in India," Chidambaram told the BBC.
"There have been three major attacks in India recently -- in Pune, Mumbai and Delhi," said Chidambaram. "In respect of the Mumbai and Pune attacks, we are fairly certain they were carried out by Indian modules or India-based modules."
India often has suspected Pakistani groups of setting off bombs in India, including the devastating Mumbai bombings in 2008 in which 170 people died.
"That threat remains but we must also look at Indian modules or India-based modules which are capable of carrying out terror attacks," he said.
Police have refocused efforts on groups operating in India, he said.
Chidambaram's interview with the BBC is his first with a media outlet since the court bombings, the BBC said.
As with previous home ministers, Chidambaram has suffered criticism over perceived failures to prevent terrorist attacks. He took office in November 2008 when Shivraj Patil resigned over such criticism in the wake of the 2008 Mumbai attack.
Patil said that he felt obliged to take "moral responsibility" for the brutal attacks in Mumbai, the Times of India reported at the time.
Chidambaram also has tried to tackle the communist Naxalite Maoist insurgency in eastern India but with varying degrees of success despite sending more soldiers and beefing up local and state police forces.
Last year there were several major attacks by Maoists including a train derailment in May that killed more than 150 people. An attack the following month left 26 policemen dead. This year Maoists notably dismembered 10 police officers in Chhattisgarh state.
The most recent criticism surrounds the bombings in Mumbai in July. Three bombs -- at the Opera House, the Zaveri Bazaar and at a bus stop -- killed 26 people and injured 130.
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