RIVER FALLS, Wisconsin (CNN) -- A 34-year-old father was being held by authorities Wednesday in connection with the deaths of his three daughters, who were found inside his ex-wife's Wisconsin home with the gas fireplace turned on, officials said.
Aaron Schaffhausen of Minot, North Dakota, is expected to be arraigned Thursday, said officials in River Falls, Wisconsin.
Formal charges are pending, and Schaffhausen is being held in the St. Croix County Jail, officials said.
Schaffhausen and his ex-wife, Jessica, divorced in January, and the three girls were in their mother's home with a baby sitter Tuesday when the father arrived and the baby sitter left, officials said.
The mother called River Falls police Tuesday afternoon with concerns about her three daughters' safety following statements made by the father regarding the children's well-being, officials said in a written statement.
Police found the gas fireplace turned on and smelled the odor of an apparent flammable liquid in the basement, officials said. An officer turned the gas off in the fireplace. In the home police found the bodies of sisters Amara, 11, Sophie, 8, and Cecilia, 5.
The bodies are being examined by the nearby Ramsey County, Minnesota, medical examiner's office, officials said, and results weren't available Wednesday.
Last March, the father allegedly threatened to harm one of the children in a harassment incident reported to River Falls police, officials said. Police records also show a domestic incident at the River Falls residence in August 2009, they said.
The family had lived in River Falls for several years, officials said.
The River Falls School District has arranged for counseling for families and students of Greenwood Elementary on Wednesday and Thursday, officials said.
The two older sisters attended Greenwood and "are remembered as bright, happy, friendly children," Superintendent Tom Westerhaus said in a written statement.
"The entire River Falls school family is shocked by this tragedy and deeply saddened by the loss of the three Schaffhausen girls," Westerhaus said.
Mayor Dan Toland described the incident as a tragedy.
"In these times, it is important for community members to support each other as we grieve the loss and deal with the shock together," Toland said in a release.