Sources claimed there were two facilitators of the suicide bomber: one brought him to Islamabad on 23 December and the other handed him the suicide jacket in Rawalpindi.
According to preliminary investigations, the suicide bomber had traveled to Mardan from Karak, stayed there overnight along with one of the facilitators, and then moved to Swabi where both took a vehicle to reach the Pirwadhai bus terminal in Rawalpindi.
So far, it has yet to be ascertained if they had traveled with a ready-to-detonate suicide jacket - which would be very risky and dangerous - or if they assembled it elsewhere.
It is believed that there was another facilitator present in Rawalpindi, in close proximity to the bus terminal, who brought the jacket to the bomber.
Sources say the bomber also made a call to someone after reaching Pirwadhai. It is suspected that the man to whom the bomber had talked was the one who had arranged the suicide jacket.
Investigators had reportedly found some remains of the bomber from the crime scene, including four of his fingers.
Forensic experts succeeded in obtaining fingerprints from them, resulting in a positive identification. A SIM found from the spot also apparently had the same profile as those taken from the fingerprints.
The suicide bomber was reportedly a native of Kurram tribal district of Khyber Pakhtunkhwa, and has been identified as 22-year-old Saqibuddin.
Meanwhile, a man who made a video of Parliament House from Margalla Hills and shared it on social media with the threat of terrorism has been arrested, the sources said.
The arrest was made with the assistance of intelligence agencies, and the suspect is said to be affiliated with the banned Tehreek-e-Taliban Pakistan (TTP).