CHICAGO — A proud father visiting his son in Afghanistan spent what would become both men’s final days seeing the city where the younger man ran a small clinic, drinking tea with a university colleague and learning about his son’s work.

A planned visit to a Kabul hospital brought them together with a third Illinois man, a doctor who shared their interest in the Afghan people and a faith-driven commitment to helping others.

Gary Gabel of suburban Chicago and his son, John Gabel, were killed Thursday when an Afghan police security guard opened fire as they entered the grounds of a hospital in Kabul. Also killed was Dr. Jerry Umanos, a pediatrician from Chicago. John Gabel’s wife, Teresa, also an American, was wounded.

Although Umanos had been identified as one of the dead, the identities of the other three Americans had not been released until Saturday.

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What prompted the guard to fire on the Americans was not clear, but recently there have been a number of so-called insider attacks, incidents in which Afghan security forces fire on comrades or foreign trainers or civilians. Violence increased in Afghanistan ahead of the NATO withdrawal and in the weeks leading up to the country’s April 5 election.

Whether John and Teresa Gabel’s young daughter, Laila, and John Gabel’s mother, Betty, were along for the visit to the Cure International Hospital in Kabul that day remained unclear Saturday. Umanos, who trained young doctors and cared for pediatric patients at the hospital, had invited the family as his guests.

“Giving back to those in need was special to all the Gabel family,” Arlington Heights Mayor Thomas Hayes said. The mayor said he’s known the family for 25 years as members of the Orchard Evangelical Free Church in Arlington Heights, Ill., and learned of the deaths first “through the church grapevine” and then from a church email to members.

Gary Gabel sang in the church choir, was involved with church youth groups and the leadership team. Hayes coached John and his own son, both now in their early 30s, when they played on a church basketball team.

Hayes described the church as a close-knit group that has grown over at least four decades to 2,000 members in four suburbs. “It’s going to be a very difficult time tomorrow morning, I can tell you that,” Hayes said of Sunday’s church service.

Family and friends grieved privately Saturday.

Kabul University Vice Chancellor Mohammad Hadi Hadayati remembered John Gabel as a “good friend” who worked for the charity Morning Star Development and ran a small health clinic that provided a pharmacy and emergency care for the students, professors and employees.

John Gabel had directed the clinic for two years under an agreement between Kabul University and Morning Star, Hadayati said.

“We have lost a great man, a great teacher, a man who was here only to serve the Afghan people,” said Hadayati, who had lunch with the whole family the day before the attack. “I was very honored to meet John’s parents,” Hadayati said. “Both his mother and father were so proud of their son.”