The marksman also told the hearing he felt “very vulnerable” when navigating through Borough Market searching for the attackers.He said: “There was just myself and (a colleague), lots of openings and exits, lots of corners… The fear was the terrorists could be anywhere within the vicinity.”The terrorists were killed in a hail of gunfire, with one stray bullet hitting and injuring pub-goer Neil McLelland in the head.The inquest has heard Butt, 27, Redouane, 30, and Zaghba, 22, were in “attacking mode” when they ran towards armed officers on the evening of June 3 2017.The inquest continues. Earlier, BY5 had recounted firing three shots at ringleader Khuram Butt, “until he stopped moving”. Police marksmen who thought injured London Bridge terrorists would kill them by detonating suicide belts have described firing shots until they “stopped moving”.Metropolitan Police officers, known only as BY5 and E59, told the Old Bailey they feared for their lives and explosives would have killed them if set off.E59 said he came across Rachid Redouane and Youssef Zaghba lying on Stoney Street, both of whom had already been shot, with Zaghba in a “crucifix-type position”.The officer, a firearms specialist since 2009, told the attackers’ inquest: “I saw Redouane start to move… it looked to me as if he was reaching around to the strap with his right hand toward that strap.”I thought the strap was part of his IED (improvised explosive device) and I believed he was making efforts to detonate that IED… I thought we would die.”I then fired shots at Redouane. I fired four shots. They were fired in fairly quick succession.”The three attackers wore fake explosives belts as they carried out the 10-minute van and knife rampage which left eight people dead and 48 injured. The armed policeman, who had 11 months’ experience in the role at the time, said: “He (Butt) was sort of laying face down.”Immediately I was concerned that I was within the blast radius of the device. He made a significant movement trying to get up from the prone posture.”I believe I was shouting at him to remain still. I was shouting at the top of my lungs repeatedly. Unfortunately he’s still moving so I took a number of shots in his direction.”I believed he was going to try to detonate the device around his body.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.