Paratroopers were sent into the Bogside on Bloody Sunday without specific clearance from either the senior army commander on the ground or army headquarters, it was argued at the inquiry yesterday.
Counsel for relatives of the victims said that someone within the Parachute Regiment itself took the decision, and that the command headquarters was kept in ignorance of what was happening for almost an hour.
Mr Arthur Harvey drew on army logs and records of military radio messages on the day to support his submission that units of 1 Para (the 1st battalion of the Parachute Regiment) launched a supposed "arrest operation" without proper authorisation.
Thirteen people were shot dead by the paratroopers and a similar number were wounded shortly after the soldiers rushed in, but the army's tactical headquarters outside the area appeared to have been given no details of what was going on.
Thirty-three people were arrested by the paratroopers in what Mr Harvey suggested was an indiscriminate "scoop-up" operation rather than a targeted arrest operation aimed at rioters.
These people, many of whom had been tending to the wounded and dying or taking them to hospital, were described on army documents as having been arrested for "riotous behaviour" and in many cases the arresting soldier simply stated: "He was in a group in a house."
Counsel added: "It also means that in terms of those who were arrested, the persons in charge of them had in contemplation a massive campaign of perjury to persuade local magistrates that these individuals should be convicted."
Mr Harvey said that radio communications on the day were supposed to be directed through headquarters. But the various logs showed that it was never communicated to Brig MacLellan, the senior commander on the ground, what precisely the sub-units of 1 Para were doing. Brig MacLellan in turn had a duty to keep Headquarters Northern Ireland informed of what was going on.
But for a period after 4 p.m. on the day, Brig MacLellan "simply does not know where support company (of 1 Para) are because no one has told him," said Mr Harvey.
The position as far as 8th Brigade (commanded by Brig MacLellan) was concerned - and the information it was supplying to HQ Northern Ireland - was that by 16.17 hours no arrests had been made, indicating either that 1 Para had stopped or that it had been ordered to withdraw.
Mr Harvey suggested that during this period the tactical command of 1 Para had been dealing directly with units of other regiments instead of going through brigade headquarters.
A message to brigade headquarters just after 16.26 hours said that two civilians were lying wounded or dead and that "who shot them we do not know". But by this stage, Mr Harvey suggested, support company of 1 Para had shot dead at least six people, and had probably also killed six others.
Counsel said that questions to be determined were: was an order to go in ever given; if so, how was it transmitted and in what terms was it given, and if so, at what time was it given.
The inquiry will resume on Monday.