According to the residents of Delhi's Rohini area where the blast happened, there was a "chemical-like" smell at the site and thick white smoke everywhere for 15-20 mins after the blast.
Some localites living up to 200-250 metres away from the site described the the blast as an "earthquake-like" shock.
The sound of the blast was heard several hundred metres away.
Forensic experts found a suspicious "white powder" at the spot and have sent it to the laboratory for examination.
"The white powder could be a mixture of ammonium nitrate and chloride. There was a foul smell of chemicals after the blast. Local residents and police officials who rushed there also felt the same," a senior police officer said. The officials are suspecting a crude bomb could be the reason for the blast.
As per a PTI report, sources in Delhi Police said that it was a low-intensity IED (Improvised Explosive Device) controlled with a timer or remote without shrapnel or ball bearings.
The matter took a new turn when a pro-Khalistani Telegram group called Justice League Indian claimed responsibility of the explosion.
The group in a post claimed that the blast was carried out in retaliation to the "targeting" of pro-Khalistan separatists allegedly by Indian agents.
The post surfaced on social media late on Sunday evening pointing to the possible involvement of pro-Khalistani separatists behind the blast. Police have sought details of the handlers of the group from Telegram.
According to a police officials, the CCTV of the blast was shared with a Khalistan Zindabad watermark on it in the Justice League Indian Telegram channel.
A Telegram post by the group read, "If Indian coward agency and their master think they can hire filthy goons to target our members to silence our voice then they live in fools world. They can't imagine how close we are to them and how capable we are to strike anytime #KhalistanZindabad #JLI."
PTI sources said that police have recovered a CCTV in which a suspect in white T-shirt is spotted on the spot, a night before the blast.
The suspect is likely to have planted the explosive a night before the blast.
A senior police official told news agency PTI that it is suspected that the perpetrators carried out the blast to send a message to the authorities.
The perpetrator "intentionally" selected the spot to not harm the people but to give a message, the officer said. It is suspected that an Improvised Explosive Device (IED), wrapped in a plastic bag, was hid in a one-feet-deep pit near the CRPF school wall, the officer added.
The incident comes against the backdrop of a series of bomb threats sent to several airlines in the last few days.
The CRPF officials from the Institute of IED Management, Pune have conducted a ground assessment, while the NSG's Bomb Disposal Squad (BDS) is preparing to submit its final report to the Delhi Police.
The Delhi Police, in turn, is expected to submit its initial report to the Ministry of Home Affairs (MHA). Additionally, the NIA (National Investigation Agency) and the Forensic Science Laboratory (FSL) of the Delhi Police have been assisting in the investigation.
(With PTI inputs)