The Walmart was still closed as of Thursday morning, Thornton Mayor Heidi Williams said.
In a statement, Walmart spokesman Ragan Dickens said the store’s employees are all accounted for and safe.
“We are relieved that an arrest has been made in this case,” he said. “Our thoughts and prayers continue to be with the families who lost loved ones and on supporting our associates. We will continue assisting law enforcement however we can.”
Police have not released a motive for the shooting.
Moreno was a well-known fixture at the Auraria Higher Education Campus, a large college in downtown Denver where he worked for 18 years. He worked as a structural tradesman, doing repairs of various kinds, spokesman Blaine Nickeson said.
“He had a lot of staff and faculty on campus that relied on him and felt like he was someone who gave them great customer service,” Nickeson said. “He was easy to engage with and always had a smile on his face.”
Vasquez was a father with two little girls and another child on the way, according to a GoFundMe site set up to raise money for his family.
According to public records, Ostrem worked in the construction industry, including as a sheet metal fabricator. Over the years, he started at least two businesses that are now delinquent, according to the Colorado Secretary of State. Ostrem frequently moved, most recently settling in a drab apartment building on Samuel Drive in Denver. In 2015, Ostrem filed for bankruptcy.
In 2013, Ostrem was arrested in nearby Wheat Ridge for driving under the influence of alcohol, according to police records. Court records also show that he was charged in 1999 with resisting arrest, a charge that was later dropped.