Jamison Childress, 20, was shot in the head by agents at a B.C.-Washington border crossing on Thursday, after spraying an agent with an unidentified chemical.
He was wanted by police for first-degree murder in relation the killing of Brando Walker, 18. Walker's body was found by fishermen in the Elbow River on March 7.
Walker was killed in a home in the northeast Calgary community of Saddleridge but police have not said how his body ended up on the reserve.
RCMP won't comment on motive but say it was not a random attack.
"Brando Walker was known to these individuals," said Cst. Jason Curtis. "They were associates, all we know is that this was not a random act, they were known to each other."
The three remaining suspects are young men between 15 and 21 years of age.
They will appear in Calgary court next week to face various charges including second-degree murder, manslaughter, and accessory to murder.
RCMP have interviewed about 100 people as part of what they've described as a complex investigation.