It also said in a statement issued late on Monday (local time) that it had arrested another of Nabi’s alleged accomplices from Kashmir.
The agency said Jasir Bilal Wani had “allegedly provided technical support for carrying out terror attacks by modifying drones and attempting to make rockets” before the blast.
An AFP photographer earlier saw Ali being taken under heavy guard from a police truck to a New Delhi court to face charges.
Indian media reported that the court had ordered that he be held in custody by the NIA for 10 days.
‘Prepared for the future’
The blast erupted near a busy metro station close to the Red Fort in Old Delhi, from where the Premier’s annual Independence Day address is delivered.
Prime Minister Narendra Modi has called the attack a “conspiracy” and vowed to bring the “perpetrators, their collaborators and their sponsors” to justice.
Nabi was a medical professor at a university in Haryana state, just outside the capital, while Ali had allegedly travelled to Delhi to “facilitate the purchase of the car which was eventually used as a vehicle-borne improvised explosive device [IED]”, according to the NIA.
India has provided no further information on the alleged motives or network behind the suspects.
The bombing was the worst attack since April 22, when 26 mainly Hindu civilians were killed at the tourist site of Pahalgam in Indian-administered Kashmir.
New Delhi accused Pakistan of backing that attack, claims Islamabad denied.
India launched strikes inside Pakistan in May, triggering four days of intense cross-border conflict that killed at least 70 people.
Modi vowed after a ceasefire that “any attack on Indian soil will be considered as an act of war”.
Army chief General Upendra Dwivedi also issued a pointed warning to Pakistan on Monday, comparing the brief May conflict to a “trailer” rather than a full-length film.
“I’d like to say that the movie hasn’t even started – only a trailer was shown, and, after the trailer, it was over within 88 hours,” Dwivedi said in a speech at a defence conference in New Delhi.
“So, we’re fully prepared for the future, and if Pakistan gives us such an opportunity, we’d like to provide them with a thorough education – on how a responsible nation should behave with its neighbours.”
-Agence France-Presse