Suicide bombers triggered explosives in churches and hotels in the country, killing some 290 people and leaving hundreds of others injured.
Kowalski was on a business trip and checked into the Cinnamon Grand Colombo in the early hours of April 21. He was killed later in the day in a blast set off by a suicide bomber who was standing in the buffet line at the hotel's restaurant.
Kowalski posted on Facebook on April 19 from Denver International Airport, showcasing his flight and saying: "And the fun begins. Love these work trips. 24 hours of flying. See you soon Sri Lanka!"
In a Facebook post on Monday, his brother confirmed that Kowalski was among the victims.
According to Kowalski's LinkedIn, he worked for education technology company Pearson. The company also confirmed his death on Monday in a note to employees.
"Colleagues who knew Dieter well talk about how much fun he was to be around, how big-hearted and full-spirited he was. They tell of a man to whom we could give our ugliest and most challenging of engineering problems, knowing full well that he would jump straight in and help us figure it out. Dieter, they tell me, was never happier than cheer-leading for our customers and our company and inspiring people in the best way he knew how—by helping them to fix things and doing it with joy, happiness, and grace."
Fallon continued: "We’re angry that a good man, who took simple pleasure in fixing things, has been killed, along with many others, by evil men and women who know only how to destroy.”
Kowalski also worked for Spectrum Real Estate in Denver and posted pictures of houses he was working to sell on his social media page. It said he was from Milwaukee, Wisconsin.
In 2016, Kowalski posted pictures from another trip to Sri Lanka, including photos of him at various tourist sites such as Sigiriya and one of a monkey perched on a rock.
Eight British citizens, at least one other American, and citizens from Denmark, India, Turkey, and the Netherlands were among the 290 victims, along with many Sri Lankans. Another 500-plus were injured by the blasts.
Several Canadians were also killed in the attacks, including M. Lahiru, Lahiru's wife M. Diliniee, and Sudhiva Fernando.
"It's indescribable."
Fernando said that he and his family moved to Canada in 2007 from Sri Lanka but some family members still live there. The family is Christian and had been fasting for two days in the lead-up to Easter.
"Sunday is the day that we celebrate. It's the day that we're back on our feet and we celebrate, we have a big mass," he said. "For something like that to happen on today of all days, it just hurts that much more."
Samith Warnakulasuriya, another Canadian, said that several family members were inside St. Sebastian's Church in Negombo and were killed in the attack. His parents and sisters were just outside the church and survived the bombing.
"I came home and I was shivering ... My family members, nobody would have been thinking about any kind of explosion in the churches, where people pray to God," he said. "We are there for peace, for security."