Thursday’s suicide attack on the Central Reserve Police Force (CRPF) convoy suggests a van or small car may have been used as the car bomb, and the explosive may have been a mixture of RDX and Supergel-90, a blasting agent commonly used in quarrying, according to officials aware of the preliminary investigations. The investigators believe at least three to four people are suspected to be involved, including a bomb-maker and spotters who would have tipped off the bomber, Adil Admad Dar, about the movement of the convoy.The clues are only a part of several critical questions being asked in the wake of what is the deadliest attack on security forces in Jammu and Kashmir, the chief among which are how it could take place without being intercepted and who are the main players. “Investigators recovered a bumper of a Maruti vehicle from the blast side. It could be of an Alto or an Eeco. Besides the bumper, no other discernible part including the registration details of the vehicle has been found so far,” said an official from a counter-terrorism agency involved in the investigation, asking not to be named. Initial reports had suggested the vehicle may be a Mahindra Scorpio. Also watch: ‘Big mistake’: PM Modi’s stern warning to terror outfits The official quoted above said the attacker was waiting for the convoy on an approach road to the Jammu-Srinagar highway on the Kakapora-Lelhar side. “The attacker entered the highway from left and when the CRPF bus was alongside, he detonated the vehicle filled with RDX mixed with Supergel-90,” he added, citing some of the findings from forensic analysis of the site. The impact of the blast was in a radius of around 150 metres, the analysis suggested.“A team of the National Investigation Agency (NIA) along with the explosives and forensics experts collected materials required for evaluation of the crime scene. Considering the status of the site, the team would continue sifting the material tomorrow as well. More will be made known after the analysis is over,” said a spokesperson of the NIA, which reached Pulwama on Friday. Terror group Jaish-e-Mohammad (JeM) said its operative carried out the attack and identified the man as Dar, a 22-year-old south Kashmir resident who lived roughly 10km away from where he attacked the CRPF convoy, killing 40 troopers had died as the bomb tore through a bus, reducing it to a heap of twisted metal and spreading human remains in a radius of around 80 metres.A senior explosives expert in the security establishment explained that Supergel-90 “acts an incendiary device and can multiply the potency of the main explosive”.A CRPF official said the bus that came under attack was fifth in the convoy, with the next bus travelling at a distance of around 50 metres behind. All 39 travelling in the bus number five died in the attack, while another CRPF trooper, who was part of the Road-Opening-Party stationed on the highway, was also killed.“Five CRPF personnel travelling in bus number six too got injured in the attack but their condition is stated to be out of danger,” said a CRPF official, who spoke on the condition of anonymity. Following Thursday’s attack, officials are likely to restrict civilian traffic on roads when security forces are being moved. “Before 2003, no civilian movement was allowed when security convoys moved. But due to complaints , the rule was eased,” said a Srinagar-based security official who spoke on the condition of anonymity.Investigators are also looking at the pattern of movement of paramilitary convoys between Jammu and Srinagar, which is currently fixed. Meanwhile, the Indian Army tweaked its “Standard Operating Procedure” (SoP) of convoy moments. All formations have been sensitized and asked to keep its convoy movements as unpredictable as possible, and also limit movements unless absolutely necessary.