Three children were killed after their mother’s car rolled into an iced-over pond last week, Michigan authorities have said. The brothers, ages 4, 3, and 1, were trapped in the SUV after their mother veered her vehicle into oncoming traffic on Thursday, according to Ottawa County police. It is not yet clear why, a spokesperson told CNN, but there was no evidence that the woman was driving under the influence. Her car then went over a curb and crashed, upside-down, into the retention pond. The mother, an unidentified Holland Township resident in her thirties, was able to escape. But the boys, strapped into car seats, remained in the vehicle, which was partially submerged in less than four feet of water. First responders on the scene were able to remove the children from the car, but roughly 12 minutes had passed by the time all were free, according to a local CNN affiliate. All three were later pronounced dead at nearby hospitals. “It’s just an unbelievable, tragic loss,” Ottawa County Sheriff Steve Kempker said.