But Maj. Dan Dandurand was unable to tell a public inquiry what relevance the note had to an investigation that was already closed.
Langridge hanged himself in barracks at the Edmonton garrison in March 2008 and left a suicide note that asked his family for a small, private service, although his mother and stepfather consented to a military funeral.
The family wasn't aware of the note until a board of inquiry was convened to investigate the Afghan veteran's death.
Evidence put before the Military Police Complaints Commission shows investigators were reluctant months after foul play was ruled out to release the note to both an army investigative board and the family because it was material to the case.
"At this point in my mind, it was still classified as evidence," Dandurand told the inquiry Wednesday.
"Of what?" said commission lawyer Mark Freiman.
Dandurand replied it was "simply a classification, not necessarily of anything," an answer that seemed to mystify Freiman.
"But isn't evidence defined as information or a thing that tends to prove or disprove at matter at issue in a criminal investigation? And there was no criminal investigation ongoing," the inquiry lawyer asked.
"No, there was not," Dandurand said.
He later testified that his understanding of the classification of evidence and how long it must be held are "now much different."
Sheila and Shaun Fynes, Langridge's parents, were provided with a photocopy of the note, and military policy required them to file a formal access-to-information request in order to get the original.
The military eventually changed that policy and many government witnesses have apologized for the omission, which the family says is evidence the National Defence investigation was biased.
Freiman led Dandurand through an email chain where his superiors explained to officials in Ottawa that investigators believed it wasn't in the interest of relatives to see the note because it would cause emotional distress.
Dandurand seemed startled and said he had "no understanding of why we would say" that.
Other testimony Wednesday raised questions about how military public affairs officers characterized the case when a journalist began asking questions.
Documents tabled with the commission show media lines prepared in the event of questions claimed military police had apologized to the family when it had not.