Church members at St Stephen's Episcopal Church in the Birmingham suburb of Vestavia Hills were spared further violence on Thursday evening when someone at the dinner subdued the gunman and held him until police arrived.
The suspect, Robert Findlay Smith, was on Friday charged with capital murder, Jefferson County District Attorney Danny Carr said in a statement.
The baffling violence in a wealthy suburb outside Birmingham left victims' families in disbelief and deepened unease in a nation still reeling from recent rampages by gunmen at a Texas school, a New York grocery store and a church in California.
Two of the Alabama shooting victims were 84 years old, the third was 75.
St Stephen's was Walter Bartlett Rainey's favourite place, a church that "welcomes everyone with love", according to his family.
They said in a statement on Friday it was hard to believe he was killed attending a church dinner with his wife of six decades.
"We are all grateful that she was spared and that he died in her arms while she murmured words of comfort and love into his ears," said the statement provided by 84-year-old Rainey's daughter, Melinda Rainey Thompson.
Police said Sarah Yeager, 75, of Pelham died soon after being taken to a hospital on Thursday.
The third victim, an 84-year-old woman, died on Friday. Police did not immediately release her name, citing a request by her family for privacy.
More people would have been killed or injured had the shooter not been stopped, Vestavia Hills Police Captain Shane Ware said.
"It was extremely critical in saving lives," Ware told a news conference. "The person that subdued the suspect, in my opinion, was a hero."
Ware said police are still investigating what motivated the suspect, who occasionally attended services at the church.
Authorities executed a search warrant at Smith's home, located less than five kilometres) from the church.
A mugshot distributed by police shows the 70-year-old suspect with a blackened left eye and cuts to his nose and forehead.
Records from the Bureau of Alcohol, Tobacco, Firearms and Explosives show Smith is a licensed gun dealer whose business address is the same as his home address. Court records show Smith filed a lawsuit against Samford University, a private university in metro Birmingham, in 2008 in which he alleged campus security wrongly detained him and accused him of impersonating a police officer.
Vestavia Hills Mayor Ashley Curry told reporters his "close-knit, resilient, loving community" had been rocked by "this senseless act of violence".
There have been several high-profile shootings in May and June, starting with a racist attack on May 14 that killed 10 Black people at a supermarket in Buffalo, New York.
The following week, a gunman massacred 19 children and two adults at a primary school in Uvalde, Texas.
Thursday's shooting happened just over a month after one person was killed and five injured when a man opened fire on Taiwanese parishioners at a church in Southern California.
Agents with the FBI, U.S. Marshals Service and the Bureau of Alcohol, Firearms, Tobacco and Explosives joined investigators at the scene, which remained cordoned off on Friday with yellow police tape as police vehicles with flashing lights blocked the route to the church.
Alabama Governor Kay Ivey issued a statement late on Thursday lamenting what she called the shocking and tragic loss of life.
"This should never happen - in a church, in a store, in the city or anywhere," she wrote.
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