Video report by ITV News Correspondent Emma Murphy
A former soldier was among those who tried to help Pc Keith Palmer after he was stabbed in Westminster's terror attack on Wednesday.
Tony Davis was the first civilian to reach Pc Palmer in the aftermath of the attack, and was joined by police officers and medical staff who fought in vain to save him.
Mr Davis, who had been leaving parliament when events unfolded, said he "just did what anyone else would have done."
He described how he saw the attacker strike the policeman with two big knives, and an armed marksman shoot the man down.
"At that time, I just turned my attention to the policeman."
Mr Davis said: "He's a fellow Brit, just doing his job. You just want people like that to pull through."