A post-mortem examination showed Mr Mousa had at least 93 injuries
An Iraqi man has told a public inquiry he heard his friend beg for mercy while they were both being detained by British soldiers.
Witness D1 said he heard the voice of Baha Mousa when they were held in a detention centre in 2003.
In a statement D1 said he had known Mr Mousa, who was 26, for a long time "and could recognise his voice".
Mr Mousa died while in custody and the inquiry is being held to establish the circumstances surrounding his death.
The witness worked as a cleaner and guard at the Ibn Al Haitham hotel in Basra, southern Iraq.
Mr Mousa and nine other civilians were arrested at the hotel in Basra on 14 September 2003.
Soldiers from the Queen's Lancashire Regiment, which has since been amalgamated, found weapons on the premises.
The witness told the inquiry: "On the evening of the second night, everyone was screaming, then some time during all this commotion, I remember hearing Baha Mousa's voice.
"I knew it was Baha because I had known him for a long time and could recognise his voice.
"It seemed as if he wasn't that far away from me and the other detainees. I heard him crying out something like, 'I am very tired, I can tolerate no more, please give me five minutes. Have mercy on me, I'm dying. I'm about to die, help me'.
"Then after a while I did not hear Baha scream out any more."
Describing the men's treatment, the witness said: "I was terrified, I was afraid, I was in pain.
"I was afraid that I would be beaten at any minute."
The witness told the inquiry, in London, that two Kalashnikov guns were kept in the hotel for security, but he did not know anything about the other weapons and fake identity cards.
The inquiry has already heard Mr Mousa had been working as a receptionist at the hotel for less than a month when he was arrested by British soldiers.
The father-of-two died at about 10pm on 15 September 2003 having suffered 93 separate injuries, including fractured ribs and a broken nose.
Another detainee, hotel co-owner Ahmad Matairi, gave evidence to the inquiry and told how soldiers had gambled on whether they could knock him down when they hit him.
In a written statement he said: "As I understand a little bit of English, I could tell that the soldiers were taking bets as to who could make me fall down.
"After hearing this, a soldier punched my back around my kidney with such great force that it caused me to fall to the floor in pain.
"When I fell down, the soldiers started to laugh and shout as if they had achieved what they wanted."
When asked why he had not mentioned this in previous interviews with the Royal Military Police (RMP), he insisted he had said it but it may have been lost in translation.
Mr Matairi was asked if his hotel had been used as a meeting place for Saddam supporters in Basra.
He said: "I have no idea of that. I am against the previous regime. I have a brother who was executed by the regime."
When shown photographs of weapons, including grenades, that were found in a hotel toilet, he said he knew nothing about them and that another of the hotel's owners, named only as C1, had a key to that room.
He said he was later questioned by a man he referred to as "a very senior British commander" who asked him where C1 was and told him he would be released if he told him.
When asked why his written statement to the inquiry and a statement given to the RMP were contradictory, he said: "This is not my statement. They just took my signature."
The inquiry also saw still images from a short video showing one soldier, Cpl Donald Payne, with the prisoners.
Cpl Payne became the first member of the British armed forces to be convicted of a war crime when he pleaded guilty at a court martial in September 2006 to inhumanely treating civilians.
He was dismissed from the Army and sentenced to one year in a civilian jail.
Six other soldiers who faced the court martial were all cleared on all counts in March 2007.
The inquiry continues on Tuesday.