Seven residents and one police officer were injured in the highrise building in the city's West End during the attack Thursday night.
Police said it appeared a male suspect, who was not a resident of the building, ran through the hallways slashing residents who police believe had no connection to him.
"He was in the building before this started. They're looking today at why he was in there," said Vancouver Police Sgt. Randy Fincham.
"It was something that happened in the building where he started this rampage and went floor to floor in the building and committed these random acts of violence against people that were already in the halls."
It is a "fairly significant crime scene and a lot of evidence to gather," Fincham said, adding that investigators are looking at whether mental health issues, drugs or alcohol may have played a role in the attack.
The suspect's name was not released.
A resident of the building said he heard screaming shortly before 7 p.m. a few floors below his suite.
"I got out of my apartment to check what was going on in the courtyard and there was definitely a commotion. At this point we didn't really know the extent of the attack," said the man, who did not want his name published.
Police arrived and blocked off all the entrances, he said.
"(We) saw five people taken away on stretchers," he said. "I think at that point, when we saw them, it really hit us that this was serious."
There are children living on the ground floor, and he said he was relieved to find out none of them were harmed.
Police kept the building secured for some time, he said.
"After that we were just stuck there, some of our neighbours couldn't get into their units so we opened our doors for them to stay with us at least until they could get in," said the resident, who is not convinced the attack was as random as first believed.
"While I didn't recognize the suspect they took into custody as someone who lived here, this guy knew someone in the building... It wasn't just someone off the street who jumped in. That's my feeling. The building is really safe, the tenants don't just let people in. We're a family building."
Another resident said she heard a commotion and thought a couple was fighting. Then she heard people running in the hallway outside her door.
"I didn't want to open the door. I didn't know what was happening," said the 61-year-old.
She gathered information from television and radio reports but had not spoken to police, through they remained in the building through the night.
Fincham said six people were taken to hospital. Two were released by Friday morning and one woman remained in critical condition.
Another bystander was treated at the scene and released. One police officer was also treated at the scene for injuries suffered during the arrest.
The 33-year-old suspect was taken to police cells on Thursday night, and was expected to appear before a judge late Friday. Charges had not yet been filed.
"We will be asking that he's not released back into the community," Fincham said.
Possible charges could include assault with a weapon, aggravated assault or even attempted murder, police said.
Social media erupted Friday with discussion of the attacks, with many users expressing relief that the suspect did not have a gun. Fincham agreed.
"It appears this person used whatever tools he had access to, to do the damage that he did in that building," he said. "I'd hate to see how much damage would have been done if this person had access to a firearm."