A father in Arizona who left four children and a young relative at home so he could buy Christmas gifts and groceries returned to find the charred remains of the family’s home after a fire broke out, killing all five children inside, authorities said.

Investigators in northwestern Arizona said Tuesday they have yet to determine what started the blaze, which began Saturday evening in the downstairs foyer area of the two-story duplex. Flames and smoke traveled up the only staircase inside the home, preventing the children from escaping.

Their bodies were all found in an upstairs bedroom, investigators said.

Bullhead City police did not immediately release the names of the children pending identification by the medical examiner. They included a 4-year-old girl and her three brothers — ages 2, 5 and 13 — and an 11-year-old boy who was a family relative and visiting at the time.

City Mayor Steve D’Amico, in a video statement Tuesday, said the tragedy has shaken the close-knit community near the Colorado River and the Nevada border.

“I have seen the flowers, the stuffed animals and the candles” lining the chainlink fence in front of the home, D’Amico added.

Patrick O’Neal was among the neighbors who rushed over after seeing smoke coming out of the home. He said about a dozen men gathered hoses and broke windows to try to get into the burning house. At the time, they didn’t know if anyone was home.

“We were screaming at the tops of our lungs,” O’Neal told reporters Monday. “We didn’t see nothing. We didn’t hear nothing. There are many guys out here who would have went into that fire if we would have known there was children … We did everything we could.”

The cause of the fire is being investigated by police and a local fire department along with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.

Bullhead City Police Chief Robert Trebes said investigators were working to get answers about the cause to “bring some closure and peace to parents and families involved.”

A memorial vigil for the five children was scheduled for Wednesday night at a nearby park while friends of the families have raised more than $11,000 as of Tuesday to help with funeral expenses.