Baikal, a 19-year-old male Amur tiger, was killed on Thursday after he got through an unlocked gate into an enclosure housing two younger and bigger male tigers.
One of the younger animals, Vasili, got into a fight with Baikal, killing the older tiger.
Zoo officials said the gate was mistakenly left unlocked.
Officials said they are investigating the incident to ensure it doesn't happen again. But Julie Woodyer of Zoocheck Canada says there should be an independent probe instead.
"I certainly would think that the best thing for this zoo to do would be to have an independent review of their safety protocols and, moreover, their animal welfare," she told CBC News.
Woodyer said there could be systemic problems at the Winnipeg zoo, citing the tiger incident as well as the sudden closure last week of the underwater polar bear viewing tunnel at the Journey to Churchill exhibit, after the bears chewed on some of the tunnel's silicone sealant.
"We've seen this kind of thing at other CAZA-accredited zoos before and, you know, they're resistant to have any kind of independent assessment done," she said, referring to facilities recognized by Canada's Accredited Zoos and Aquariums (CAZA).
Baikal is the second tiger to die at the zoo in the past two years. A one-year-old male Siberian tiger died in 2012 after he went into cardiac arrest.
Confrontation witnessed by Grade 12 students
About 20 Grade 12 biology students from Lord Selkirk Regional Comprehensive Secondary School were on a field trip to the zoo when they saw the tigers begin to fight.
One of the students, Ian Dealey, said a gate was open at the tiger enclosures when they arrived.
Dealey said it initially looked like the tigers were playing, but it quickly became aggressive and scary.
"With all the growling and noises, you never know what was going to happen to the tiger," he said.
"One of them kind of stood up and didn't want the other one there, and at one point like he kind of just puffed up his shoulders like he was going to kind of launch at his friend."
Dealey said the zookeepers were banging on the fence, trying to get the tigers' attention. The students were then asked to leave the enclosure area before the final attack took place, he added.
The students were later offered counselling services as a precaution, according to the Lord Selkirk School Division.