Sunday was a day of ever-increasing dread for friends and family of Dieter Kowalski, a 40-year-old Denver resident who was killed in the attack.

Mr. Kowalski was a senior leader of technical services for Pearson, an educational media company. He was on a business trip to Sri Lanka, where he worked with several engineering teams, according to his LinkedIn profile. It was his second visit to the country in three years, and he was planning to work alongside colleagues with whom he had become friends, said his mother, Inge Kowalski, who lives in Milwaukee.

“He was really happy to go there,” she said. “He was looking forward to the food.”

Arriving in Sri Lanka on a flight that landed several hours late, Mr. Kowalski checked into his hotel, the Cinnamon Grand in Colombo, around 5 a.m., she said.

After the bombs went off, “it was a nightmare,” she said, describing a panicked effort to find him that was reflected in the string of fearful comments beneath his last, cheerful Facebook post. “We spent the whole day yesterday looking for him.”

His family and friends hoped that he had been sleeping, rather than in line at breakfast, when the bomb went off, but no one in the United States or Sri Lanka could track him down.

They discovered that the police had his cellphone, Ms. Kowalski said, and had little luck contacting hospitals. Finally, around 10 p.m., the United States Embassy called with the news they feared most.

Mr. Kowalski went to college at the University of Wisconsin-Madison but moved to Denver over a decade ago, “for the skiing.” His mother said he was single and close to his family — Ms. Kowalski said she had just spent 10 days skiing with him in Colorado, and they had recently bought tickets for a family trip to Majorca, Spain.