More than a dozen police cars, tactical vehicles and ambulances descended on Long Plain First Nation late Wednesday and cordoned off a large area on the reserve.
Three men were seen being led out of a house in handcuffs Thursday morning, following a lengthy standoff.
RCMP confirmed late Thursday afternoon that the men — aged 20, 21 and 47 — are in custody in connection with the incident.
Many officers were still on the reserve as of Thursday afternoon, but they are staying tight-lipped about what is happening.
An RCMP spokesperson would only say the investigation is continuing.
Members of the Portage la Prairie RCMP detachment, the Dauphin RCMP's major crimes unit and the Brandon RCMP's forensic identification section are on the reserve.
Police had advised members of the media earlier on Thursday to stay far back from the "suspect area" to avoid any possibility of getting shot at.
Victim not from reserve, says chief
Long Plain Chief David Meeches told CBC News that a body was located in a ditch near a burning car at about 8 p.m. Wednesday and that the victim had severe trauma to the head.
A baseball bat was also located near the body, according to Meeches.
"I'm aware that the person who is deceased is not from Long Plain," he added, saying he can't recall there ever being such a serious incident on the reserve, located about 20 kilometres southwest of Portage la Prairie.
"We haven't seen nothing of this nature. And obviously they [RCMP] are taking it fairly serious," he said.
Meeches also confirmed that another man, who is believed to be from the First Nation, was assaulted.
News of the incident has stunned people on the Long Plain First Nation, says Juanita Bunn, who lives on the reserve.
"It's a tragedy that it happened here because everybody's so well together," she said.
"For something like this to happen here, it's crazy. Like, everybody is so shocked."
Meeches said at this point, no one seems to know who the victims were or what exactly happened.
"Until such time as I get some factual information in terms of what happened here, I don't want to speculate and I can't comment on anything that I don't know anything about at this point," he said.
"The RCMP will sooner or later provide us with specific information."