A mother who had a suspicious feeling after she dropped off her toddler at a home day care returned to the house a few minutes later to find three adults shot dead.
The woman's child was unhurt and no other children were at the day care in Brooklyn Park, Minnesota, at the time. Police are seeking a suspect in his mid-20s, believed to have fled on a BMX bicycle.
"It's a tragic day for the city of Brooklyn Park," Police Chief Michael Davis said. "We are going to bring whoever is responsible for this to justice."
Two nearby community colleges were locked down for several hours after the shootings were reported at 6.30am on Monday. Both had reopened by the afternoon, after police spent the day canvassing the area and using dogs to search for the suspect.
The Visions and Butterflies Child Care is licensed to look after as many as 12 children. DeLois Brown, 59, was listed in state records as the licence holder in good standing, with no adverse rulings or restrictions.
Police did not release the identities of the victims or the woman who found them.
Inspector Todd Milburn said the mother dropped off her child at the house and spoke with someone there. As she was leaving, she saw a man near the house on foot, and something about him raised her suspicions. "There was some reason for her to call back to the home," Mr Milburn said.
The woman called the day care and was talking to someone at the house when the line went dead, Mr Milburn said. She returned to the home and found three people had been shot. She grabbed her child and called emergency services. Police said the victims were dead when they arrived.
No one else was inside the home when the woman returned, Mr Milburn said, adding that the woman saw the same suspicious man nearby, on a bicycle, when she returned to the day care.
Police said they had no information on how many children were typically cared for at the home, or when they were normally dropped off.