The first sign was a sob that couldn't be suppressed. She tried dabbing away the tears, but they kept coming back. The more Tony Blair talked, the more the eyes of Sarah Chapman – whose brother Bob was killed in Iraq in 2005 – grew wet, her lip trembling.

She had a front row seat, no more than a few metres away from the former prime minister as he made his second appearance before the Chilcot inquiry into the Iraq war. Like the other 40 or so relatives of the dead who formed the audience for yesterday's proceedings, she had maintained a polite quiet for nearly five hours, listening to Blair's long, dextrous answers.

But that sob was a warning that the silence could not hold, that it would soon give way to a moment of astonishing emotional intensity.

When the star witness praised the armed forces as "fantastically good people – if you ask them to do something, they do it", she couldn't help herself. "Then stop trying to kill them," she blurted, earning a sharp "sssh" from Sir John Chilcot .

Soon the chairman allowed Blair to make a statement of his own, not under questioning. His face sombre, drawn despite his now permanent tan, he recalled the closing moment of his first Chilcot session 12 months ago. Then he had refused to say he harboured any regrets, a refusal the grieving families interpreted as callous indifference.

This time he wanted to make amends, declaring: "Of course I regret deeply and profoundly the loss of life."

Instantly, there was a cry of "too late" from the people seated behind him, packed together in a windowless room much smaller than it appears on television – a fact that only added to the intensity of the moment. That sparked a chorus of "too lates", most of them coming from women, bereaved wives and daughters, sisters and mothers. One called out acidly: "You've had a year to think about it."

Blair pressed on, offering his thoughts on lessons to be learned for the future. As he spoke of improved systems for the "transmission" of information to the prime minister, two women stood up and turned their backs in mute protest. After a few seconds, they headed for the door.

Sarah Chapman did not walk out but stayed put, continuing to weep, all the while touching the pendant hanging around her neck: the military dog-tag of her late brother. Blair was talking about what he called "the pain/gain ratio", the calculus a leader must consider when deciding if military action is worth it. Something in the phrase made her recoil.

And finally, after Chilcot had thanked him for his evidence, the former prime minister got up to leave. As he did, the room burst. "Your lies killed my son," shouted Rose Gentle in a loud, ringing voice, remembering Fusilier Gordon Gentle who was killed in 2004. "I hope you can live with that."

Blair did not look back, nor did he even glance sideways as he brushed past Reg Keys – the father of Lance Corporal Tom Keys – who stood as an anti-war candidate in Blair's Sedgefield constituency in the 2005 general election. "You're a disgrace to your office and to your country," Keys said, all but spitting the words.

Perhaps in anger at Blair's refusal to break his stride, one woman thundered that "He'll never look us in the eye." And then he was gone.

It was an electric close to what had seemed set to be a rather dry session, one of interest to few beyond the families in mourning and the dwindling band of Iraq obsessives. After a seemingly anxious start, Blair took to his task with complete focus, plunging again into the vocabulary that once dominated Britain's national conversation: 1441, WMD, second resolution, Blix and all the rest.

His mastery of the detail was total, flitting from ministerial minute to unclassified transcript as if from memory, with barely a peek at his notes. That extracted the odd revealing nugget – including his explanation of exactly why he felt able to ignore his attorney-general's initial legal advice – but those who yearned to see the Chilcot panel nail the former PM were once again disappointed.

It was Blair himself who was the first to jolt the proceedings with emotion. His face taut, he issued an impassioned plea for the world to get tough on Iran and for the west "to get out of this wretched posture of apology".

It was a reminder of the Blair of a decade ago, the leader who burned with such righteous conviction. But the people behind him, still weeping for their dead, were in no mood to be convinced.