A detailed forensic report carrying "critical evidence" is expected on Thursday on the blast outside Delhi High Court.
"Experts in bomb blasts who have been called from Forensic Laboratory (FSL), Gujarat are also closely examining the scene of the blast and are likely to come up with critical evidence regarding the nature of the blast soon," Chidambaram told reporters on Wednesday.
He said a detailed forensic sciences examination reports are likely to be available by today.
"Apart from the main team of 20 persons, NIA has deputed a support team of 17 officers and men to assist in the investigation. Delhi Police is working with the NIA team and are undertaking several key tasks that have been assigned to them," the home minister said.
He said that out of the 74 injured undergoing treatment, 55 are in Ram Manohar Lohia hospital, five in Sir Ganga Ram, four in Safdarjung, three each in Moolchand and Apollo hospitals, two in All India Institute of Medical Sciences, one each in LNJP and Army Research and Referral.
Chidambaram said four of the injured are in critical condition and have been admitted to AIIMS and RML hospital.
The home minister said that 17 were discharged after first aid from Delhi high court dispensary.
"Doctors are making every effort to save the lives of the injured," he said.