A firearms officer called to the scene of the Fishmongers’ Hall terror attack recalled his astonishment that suspect Usman Khan had not died, despite being shot at multiple times.

The officer, known only at Khan’s inquest by the cipher AZ99 to protect his identity, was one of six armed police to fire 20 shots at Khan during two periods of gunfire, shortly after the suspect stabbed and killed two Cambridge University graduates.

The first exchange comprised two quick shots which felled Khan, having earlier been pinned to the ground by passers by after telling them he had a bomb on him.

The second exchange, a volley of 18 shots across a period of around 90 seconds, came eight minutes later when Khan summoned the energy to sit up from his prone position on the floor where he had been seen on CCTV to be breathing deeply, writhing around, and appearing to mutter to himself.

He appeared to turn his head sideways and stare directly at the armed officers for a few seconds when he was hit by police gunfire, briefly touching a wound on his forehead before slumping finally to the ground. He was pronounced dead an hour later when the scene was declared safe.

Giving evidence to the inquest into Khan’s death, AZ99 recalled how he shot the suspect four times in the second period of gunfire, but was in disbelief Khan had not died.

AZ99 said: “He did fall back after one shot.

“Quite surreal – he put his hand towards his head, he pulled his hand away to look for blood.

“All I could think was: ‘Why aren’t you dead?’”

AZ99 said he opened fire because he was concerned Khan was reaching for a suicide belt, which was wrapped about his waist.

He told the inquest: “At that point there, I thought: ‘We’re dead.’

“This was the first movement he did that was an action rather than a reaction.

“It felt like a defined movement of: I’m now going to do something to you.”

Khan was in central London on November 29 2019 after being invited to attend an event by prison education charity Learning Together at Fishmongers’ Hall.

Police believe he travelled down by train from his home in Stafford with the fake suicide belt already strapped around his waist, while his bag contained kitchen knives bought in the days before the attack.

He stabbed Jack Merritt, 25, and Saskia Jones, 23, at the Learning Together event before being chased from the venue.

Khan had been released from prison less than a year earlier, having served an eight-year jail term for plotting a terrorist training camp in his parents’ homeland of Pakistan.

The inquest continues.