Winnipeg police have officially declared the deaths of Lisa Gibson and her two children a homicide/suicide case.

It is the first time they've spoken about it since Gibson's body was pulled from the Red River in July.

"This matter, like all homicide investigations, required in-depth investigative work surrounding forensics, as well as awaiting for time consuming crime lab results," police stated in a news release Thursday, explaining the delay.

"The criminal portion of this investigation is now concluded and based on the investigation to date, it has been determined that this matter is a homicide/suicide."

Lisa Gibson

The body of Lisa Gibson was found in the Red River several days after her children were found critically injured in the bathtub of their Winnipeg home. (CBC)

"We base our work on facts. It takes time we are entering the review stage of this file," police spokesman Const. Jason Michalyshen added during a press conference.

“At the time of the incident, it may have been very apparent to members of the public and the media what took place, but that's not good enough for us.”

Two-year-old Anna and three-month-old Nicholas were found close to death in the bathtub at the Gibson home on the morning of July 24. They later died in hospital.

Police searched the neighbourhood for days before the body of Gibson, 32, was found in the Red River, a few kilometres downstream from the home in the 100 block of Coleridge Park Drive, in the city's Westwood area.

Postpartum depression is one of the factors police said they were looking at during their investigation, but they have never commented on Gibson's mental state.

The Winnipeg Regional Health Authority reviewed its interactions with Gibson prior to its death and said Thursday that all protocols were followed for postpartum care.