Khan was killed on March 10, Kamran on March 29, Sajjad Bhat on June 18 of last year while Qari yasser was shot in an encounter on January 25, this year.
The probe into last year's Pulwama terror strike that left 40 CRPF personnel dead has virtually reached a dead end with five persons, who were either conspirators or executers of the ghastly attack, being eliminated by security forces in various encounters.
However, the case threw unique challenges for the NIA, the anti-terror probe agency formed in the aftermath of the Mumbai terror strikes in 2008, as it there is no solid information about the perpetrators or the mastermind behind the attack.
"It was a blind case for us. There were lot of murmurs but everything needs to be established beyond doubt in the court of law," a senior official, who is part of the probe, said Srinagar.
The first challenge was to establish the owner of the car used by suicide bomber Adil Ahmed Dar. There was nothing available from the vehicle which carried a cocktail of explosives like Ammonium Nitrate, Nitro Glycerine and RDX, the official said.
But with the help of forensic methods and painstaking investigations, the serial number of the car that was blown into pieces beyond recognition was extracted and within no time the ownership of the vehicle was established -- from the first to the last owner.
However, the last owner of the car, Sajjad Bhat of Bijbehara in Anantnag district, had disappeared hours before the February 14 attack and joined Jaish-e-Mohammed terror outfit. He was subsequently killed in an encounter in June last year.
"While it was clear that the suicide attacker was Adil Ahmed Dar but the same had to be established with evidence. After picking up human remains from various spots, it was sent for DNA profiling.
"The suicide attacker was identified and confirmed by matching the DNA extracted from the meagre car fragments with that of the DNA of his father," the official, who requested anonymity, said.
The role of other conspirators which included Mudasir Ahmed Khan, Qari Mufti Yasser and Kamran came to light but all of them were killed in different encounters with security forces.
Khan was killed on March 10, Kamran on March 29, Sajjad Bhat on June 18 of last year while Qari yasser was shot in an encounter on January 25, this year.
After JeM spokesperson Mohd Hassan in a video claimed that his group was responsible for the attack, it was sent for forensic examination and the Internet Protocol address was traced to a computer based in Pakistan.
The official said that during the investigation, the NIA stumbled upon another case of over ground workers of Jaish-e-Mohammed which was subsequently busted.
"Eight people have been listed in a charge sheet in this case so far," the official said.