Kirk Lackie testified Wednesday at the Military Police Complaints Commission inquiry into Cpl. Stuart Langridge's death.
The inquiry was called following complaints from his family that the investigations into Langridge's suicide were botched.
Lackie was a last-minute addition to the witness list; he asked to testify.
"I want Stu's ma and everybody to know the truth about what's going on because right from the get-go, other names have been named and whatever, and the truth has not been told," Lackie said at the close of emotional testimony.
He had met Langridge early in their training and formed a bond that later deepened over their shared struggles with addiction.
The inquiry has previously heard that Langridge drank and used drugs, and was in and out of rehab. There has also been significant disagreement about whether he suffered from post-traumatic stress disorder.
He had tried to kill himself on previous occasions.
Langridge was aware he had problems, Lackie said, but they were difficult for him to overcome.
"It's hard to think you're addicted when you are already drunk," Lackie testified.
Lackie said everyone on the base knew about Langridge's struggles, but dismissed them.
"There's a saying: the army uses you like a tissue paper. As soon as they're finished with you, like a tissue paper they throw you away," Lackie said.
"And Stu, was to them, a really dirty tissue paper. They threw him away, but they just didn't want to throw him away, they wanted to scoop him under the carpet."
The night before Langridge killed himself, Lackie said he tried to take him to a Alcoholics Anonymous counselling session, but the soldier refused.
The next day, Lackie was in the base's duty centre and happened to see the logbook set up to monitor Langridge.
Langridge had been placed on a suicide watch and someone was supposed to check on him roughly every 30 minutes.
That wasn't what the logbook showed, Lackie said.
"And I said to the duty driver, it's been three and half hours since someone checked on Stu. I said why don't you fly ... over there and check on him?" Lackie testified.
But elements of Lackie's recollection were questioned by both lawyers for the commission and the Crown.
Commission counsel suggested the soldiers Lackie said he spoke to that day weren't actually working, while the Crown wondered why none of the ones who have previously testified mentioned Lackie's presence on that day.
"That's because he's still in the military," Lackie replied.
Lackie said a few minutes after someone left to check, he heard sirens and then overheard an expletive-laden phone call.
He said it was then he knew that Langridge had died. The soldier had hanged himself in his barracks.
It was later that year that Lackie began a series of run-ins with the law, including one incident where he barricaded himself inside his home — with two guns, ammunition and explosives — and told police they'd have to take him out with a shot to the head.
He later surrendered without incident and pled guilty on a number of related charges. He also pled guilty to later incidents involving breaches of his probation and impaired driving.
Lackie's criminal record was cited as a concern by the Crown when it opposed his appearance on the stand.
Two Ottawa police officers were present in the complaints' commission room Wednesday, saying they were there to provide added security.
Lackie was released from the military in 2010.
Over those years, he testified that he tried to tell military personnel what happened the day of Langridge's death but no one ever contacted him.
Commission lawyers said there were no records of his attempts to contact military police.
But Lackie was finally interviewed last week.