A man arrested Wednesday and charged with the fatal shooting of a prayer leader at World Changers Church International pleaded guilty to shooting a man a decade ago in Baltimore and was committed to a mental health facility there.

Floyd Palmer, 52, calmly walked into a prayer service Wednesday morning at the College Park megachurch founded by the Rev. Creflo Dollar and opened fire as 20 to 25 people watched in horror. Greg McDowell, 39, fell mortally wounded and Palmer, a former church employee, “left just as calmly” as he entered, Fulton County police spokeswoman Cpl. Kay Lester said.

The suspect left in a black Subaru station wagon and was in the vortex of a massive police search until he was arrested without incident at Lenox Square in Buckhead just before 4 p.m.

Palmer, who resigned from the church in August for personal reasons, had been charged previously with attempted murder. In 2004 he pleaded guilty to assault charges and was deemed “not criminally responsible” and was committed, according to Maryland court records. Other records indicate that shooting occurred in 2001.

Christine Singleterry, Palmer’s former mother-in-law, said Palmer shot a man following an argument at a Baltimore mosque. “He got him to go outside and then shot him in the parking lot,” said Singleterry. She said he served about 18 months in the mental facility and was released.

“He was mixed up and argumentative,” she said.

Mack Simpson, who is married to Palmer’s sister, was shocked to hear the news. “That’s a shame,” he said. “This is the second time.”

Greg McDowell, a father of two young children, was a member of the church’s production crew and a facilities maintenance manager there, police said.

Ken Terry, a pastor at the church, called McDowell a “tremendous leader, role model and father.” He said McDowell had been a longtime member of the church. “He was faithful for a number of years. We have known him for years. Since he was a little kid.” Terry spoke of McDowell’s two sons. “He spent a tremendous amount of time with them. He was the model dad.”

Neighbors who knew McDowell said he was always friendly and always smiled and waved.