Authorities investigating an email from Harkat-ul-Jehadi Islami, the group which has claimed responsibility for Wednesday's Delhi blast, have traced it back to Jammu and Kashmir, reports say.
Various media houses received the email soon after the blast, which claimed 11 lives and injured nearly 90.
"We own the responsibility of today's blast at (the) high court (in) Delhi. Our demand is that Afzal Guru's death sentence should be repealed immediately else would target major high courts and the Supreme Court of India," the email read.
Guru has been sentenced to death by the Supreme Court after he was convicted for the December 13, 2001 parliament attack.
"We are taking the email seriously," National Investigation Agency (NIA) chief S.C. Sinha had said on Wednesday.
Wednesday's suitcase bomb went off around 10.30 a.m. just outside Gate No. 5 of the complex near India Gate in central Delhi, where passes are issued for hundreds of litigants, media personnel and other visitors to the court.
At the time of the explosion, around 300 people were waiting outside various gates of the court.
According to Home Secretary R.K. Singh, the bomb was in a suitcase.
"We have remains of the suitcase," he told reporters.
Special Secretary (Internal Security) U.K. Bansal said a preliminary probe indicated possible use of nitrate-based explosives laced with PETN. Short for pentaerythritol trinitrate, PETN is a chemical explosive that has a long history of terrorist use.