Friends have spoken of their shock after it emerged that a soldier who died at his barracks on Monday was being punished when he collapsed.
Pte Williams died in Salisbury District Hospital on Monday
Royal Welsh soldier, Private Gavin Williams, 22, of Hengoed, Caerphilly, collapsed at about 1200 BST at Lucknow Barracks in Tidworth, Wiltshire.
Five servicemen from his regiment - the 2nd Battalion Royal Welsh - have been arrested on suspicion of manslaughter.
The community of Hengoed is reported to be "devastated" at the news.
An initial post-mortem examination has been carried out but the cause of the soldier's death is not yet known, Wiltshire Police said on Wednesday.
An inquest has been opened and adjourned a Salisbury Coroner's Court into Pte Williams' death.
In Hengoed, local councillor Graham Hughes, who has known the Williams family for 35 years, said he was "absolutely shocked".
Lucknow barracks is the base for 600 Royal Welsh soldiers
He said: "The boy was only 22-years-old, one of the lads [and] fit as a fiddle.
"We've known him for a long time and we know all the family. They're a lovely family and we just can't get over what's happened to Gavin. They are absolutely devastated.
"The whole village will be devastated. I've just seen some of the headlines of the papers. You just don't think that that would happen in the British Army.
Julie Clarke, who had known Pte Williams for five years and who works at Penpedairheol's Beech Grove Social Club near Hengoed, said Pte Williams had been looking forward to becoming a soldier.
"He was very enthusiastic wanted to get on with his life, have an army career," she said. "He wanted to change his life around and was really positive. He was really into the army, it meant a lot to him.
"He was really so enthusiastic and had so much to give, it shouldn't have happened."
Ms Clarke has opened a book of condolence at the club for Pte Williams.
Labour AM Caerphilly Jeff Cuthbert said reports that Pte Williams was "beasted to death" during punishment exercises were "very disturbing".
"We understand that soldiers have to be ready for almost anything... but clearly in this instance something has gone seriously wrong and we need to know the facts so it can be sorted out."
'Hot and agitated'
Police arrested four soldiers - aged 44, 35, 31 and 28 - on Monday and have been given an extra 12 hours to question them. A 29-year-old soldier was arrested on Tuesday.
All five are being held at Salisbury.
Ambulance crews were called to the barracks and a spokeswoman for Wiltshire Ambulance Trust said that the man appeared "hot and agitated".
But she would not comment on reports that he had suffered heat exhaustion.
Police sources confirmed that officers were looking at a chain of events which led to the soldier being ordered to complete the exercise as a punishment.
Pte Williams later died in Salisbury District Hospital.