A father picking up his children on the night of the Manchester Arena attack said he thought "straight away" that Salman Abedi was a suicide bomber.
Neal Hatfield told the Manchester Arena Inquiry that when he saw Abedi in the foyer of the arena his rucksack did not look normal as it did not flex under his weight.
Twenty-two people were killed and hundreds more injured when the bomb went off as they left the concert on 22 May 2017.
"It was rock solid, that's what alarmed me straight away," Mr Hatfield said.
Mr Hatfield was about to go up the stairs to the mezzanine area of the arena's City Room when he saw 22-year-old Abedi with his back to him "in the process of lying down, he had a backpack on the floor next to him".
He told the inquiry the bag was totally disconnected from Abedi's back, adding: "It was almost as if he was trying to protect the bag and not touched it.
"I thought suicide bomber straight away, very little doubt in my mind. Honestly, my heart was racing.
"The way he was dressed, the way he was acting, the body language was that he was trying to protect the bag. He was pretending to be casual, but I could see what he was doing."
He said that he thought security stewards were having a conversation about Salman Abedi and assumed they would act.
PC Stephen Corke said that the first aid kit he was equipped with wasn't sufficient
The inquiry also heard from British Transport Police Officers, who were the first police officers on the scene after the explosion.
PC Stephen Corke had been diverted away from the Arena because of a burglary, he was meant to be back by the end of the concert but was on Deansgate when he received a radio call asking for assistance from a fellow officer.
Mr Corke said that he arrived at a scene of "utter devastation" and said it was obvious that a shrapnel bomb had been detonated and that there was no live attacker within the room.
He treated many of the injured people and said he expected there to be "swamped and flooded with medical staff" whom he thought would follow him, but didn't.
PC Jessica Bullough was the most senior BTP officer present at the arena complex that night but had only been in the job 8 months.
She took a break lasting 2 hours and 9 minutes during her shift, when it was supposed to last up to an hour - She said it was "unacceptable".
When she came back on patrol she had just missed Salman Abedi walking into the City Room.
British Transport Police PCSO Lewis Brown later said he and a colleague took a break before other officers had returned from theirs, meaning there was no one on patrol between just before 21:00 and 21:35 BST.
It was during this time that Abedi made his trip from Victoria station into the foyer.
The inquiry continues tomorrow.