Two youths with rifles retreated after being "told off" by women in the Bogside before paratroopers advanced into the area, journalist Nell McCafferty told the inquiry yesterday.
Ms McCafferty said she saw the teenagers with rifles appear out of a stairwell in some flats south-west of Free Derry Corner, where the bulk of the Civil Rights marchers had congregated to listen to a number of speakers.
"We told them to put the rifles away and clipped them round the ear. It was against the rules to carry firearms on the march and everybody knew that there was to be no shooting that day," she said.
"The two boys then disappeared back into the stairwell and shortly after this I remember Martin McGuinness arriving in the area, having been fetched by one of the women."
Questioned about this incident by Mr Christopher Clarke QC, counsel to the tribunal, she said the armed youths were told off in no uncertain terms by the women who surrounded them. "It was like two boys being caught drinking cider and their mother takes the cider off them and sends them back up the stairs where they belong - they were quite abashed."
The women had threatened the youths with Mr McGuinness, who arrived on the scene fairly soon afterwards, but the matter had been taken care of by then. Mr McGuinness looked "anxious and startled".
"Did he say anything that you recall?" Mr Clarke asked. "No, he was getting the face ate off him," Ms McCafferty replied.
She added that although Mr McGuinness was sent for, that did not mean those youths were in the Provisional IRA. They could equally have been in the Official IRA, "but Martin was what they called 'The Man'."
Mr Clarke said the tribunal knew he was the adjutant of the Provisionals at the time, and he asked if that was what she knew him to be at the time.
Ms McCafferty said she did not, but he was a man of authority in the area and a name one would know. In further replies, she said there was "a sense and a belief" that he was a member of the Provisionals, but she established that to her own satisfaction two months later when she interviewed him for The Irish Times by name.
Ms McCafferty is to continue her evidence on Monday.
Earlier yesterday, Mr Fergus McAteer described to the inquiry how, after seeing three men fall when a burst of shots rang out in Glenfada Park, he and other civilians were confronted by "incredibly agitated and excited" soldiers.
The soldiers "seemed to be crazed" and their demeanour was very frightening. After hesitating for a moment, the soldiers marched the group away at gunpoint, shouting and threatening and hitting some of the civilians.
The witness described being taken in a lorry to Fort George army base, where "one by one, we were forced to our feet, spun round and thrown off the lorry into the middle of a gauntlet".
There were troops on either side and possibly a few policemen also. "I had to run through this gauntlet of people who were trying viciously to kick and beat me," he said. "As blows rained down, I remember being hit on the knee with a baton which was very painful . . . and I was heavily kicked on the bottom of my spine."
Reaching a large shed, he was confronted by barking dogs on leads. They were made to face a wall with their hands above their heads, leaning on their fingertips. They had to face the wall for several hours.
Mr McAteer said he was formally charged with riotous behaviour. He and others received summonses and there were several petty sessions. Each one was postponed and seven months later he got a short letter saying the charges were being withdrawn.