Indian police said Friday they have detained five people for questioning as they probe rival claims of responsibility for Wednesday's bomb attack outside a New Delhi courthouse that killed 12 people.

Police investigating an email claim of responsibility arrested the owner of an Internet cafe in Indian-controlled Kashmir, his brother, and an employee. Later, two college students were also detained.

Authorities received an e-mail attributed to the group Harkat-Ul-Jihad al-Islami shortly after Wednesday's blast, which was traced to the cafe. It warned that other courts in the country would be attacked unless India repealed the death sentence given to a man convicted in connection with the 2001 attack on India's parliament.

Meanwhile Thursday, the domestic terror group Indian Mujahideen claimed responsibility for the New Delhi courthouse bombing in a separate email sent to media organizations. The group also threatened to attack a shopping mall next week.

Authorities are investigating the authenticity of both claims. Police have also released the sketches of two men seen at the site during the time of the blast, while India's National Investigative Agency has offered more than $10,000 in reward money for information on those responsible.

The bomb exploded Wednesday morning near the High Court's main gate where a crowd had gathered to enter the complex. The blast killed 12 people and injured nearly 80 others.

The blast at New Delhi's High Court was the first major terror attack in India since near-simultaneous triple bomb blasts targeted India's financial capital, Mumbai, in July, killing some 20 people. No one has been arrested in that case, but authorities say they have focused their investigation on the Indian Mujahideen group.

Wednesday's attack is the second explosion at the High Court this year. In May, a small bomb exploded outside the same court, but did not cause any casualties.