A special tactical unit used explosives to enter the building shortly after midnight and shot John Ashley to death after he opened fire, police spokesman Sgt. Clifford Gatlin said.
Police said Ashley repeatedly shot at them during the 10-hour standoff Thursday, and even shot at a remote-controlled police robot they sent inside. No officers were hurt.
"This is, it's a shock," Gatlin said. "It's big for us, because we know everybody."
Ashley, a retired city maintenance worker, was found in the back of the office, which was converted from a single-story house.
The two people police say he killed were found in the front of the building, where police rescued one of the three surviving victims Thursday afternoon. The other survivors escaped on their own.
Gatlin said investigators have learned the shooting was "a possible dispute over a divorce settlement," but that he had no further details.
He said investigators will need to speak with the three survivors to determine a motive, and at least two of them were seriously injured.
Police Chief Daren Coutee said officers called Ashley repeatedly on his cell phone and the office phone throughout the day but he refused to talk.
"We did all we could do as far as negotiations were concerned," Coutee said.
Authorities identified the dead as Camille "Joey" Giordano II, a 32-year-old assistant district attorney. The other person killed was Marty Thiels, 50, a postal worker delivering mail to the law firm.
Giordano's father, attorney Camille Giordano, also was shot. He underwent surgery and was in critical condition Friday, a spokeswoman for Christus St. Frances Cabrini Hospital said.
Also wounded, police say, were attorney Sam Charles Giordano, 49, and Andrea Fletcher Price, 27. A hospital spokeswoman said Friday that the families asked that details about their conditions not be disclosed.
"The loss of our loved one and friend and serious injuries suffered by Camille, Sam and Andrea have devastated us all," the Giordano family said in a statement. They thanked the community for their concern and sympathy and asked that their privacy be respected.
The shooting rampage near the Rapides Parish Courthouse astounded people who know Ashley in Alexandria, a central Louisiana town of about 46,000.
"I've never heard him raise his voice. I never heard of him being violent," said Charlie Gilmore, Ashley's neighbor and a local pastor.
Ashley was a deacon, sang in the choir and attended Bible study every Wednesday night at Mt. Calvary Missionary Baptist Church, said Freddie Lawson, a fellow congregant.
For the first time this year, Ashley did not show up at Bible study this past Wednesday, the night before the shootings, Lawson said.
"What his reason was for not coming, I don't know," Lawson said.
Several neighbors said Ashley smiled and waved to them on his way in and out of his one-story home, but did not socialize. Lawson, a friend for 20 years, described Ashley as jovial at church, cracking jokes and socializing.
"He'd just go around shaking hands and hugging people," Lawson said. "He was very friendly, and I'd never known him to be emotional."