They said Chairman Bill Gwatney, 49, died four hours later at University Hospital in Little Rock after the midday shooting near the state Capitol.
Witnesses said the gunman entered the party offices shortly before noon and said he wanted to see Gwatney about volunteering. Party officials said the man forced his way into Gwatney's office and fired three shots, then fled in a blue truck.
"He said he was interested in volunteering, but that was obviously a lie," said 17-year-old party volunteer Sam Higginbotham. He said the man then pushed past employees to reach the chairman's office, where he fired three times.
Gwatney, a former state senator and a Hillary Rodham Clinton superdelegate to the Democratic National Convention this month in Denver, had served 10 years as a state senator.
Clinton and her husband, former President Bill Clinton, issued a statement calling the 49-year-old Gwatney "not only a strong chairman of Arkansas' Democratic Party, but he is also a cherished friend and confidante."
After the midday shooting, the suspect was chased into Grant County, south of the capital, and apprehended after being shot. Police fired at the man but it wasn't known whether he also suffered self-inflicted injuries.
Moments before the Democratic headquarters shooting, a man with a gun threatened the building manager of the Arkansas State Baptist Convention headquarters seven blocks east. It wasn't known if the incidents were related.
Dan Jordan, the denomination's business manager, said the building manager asked the man what was wrong and that he said "I lost my job."
The state Capitol was locked down for about an hour until police got word the shooter had been captured, said Arkansas State Capitol police Sgt. Charlie Brice.
Karen Ray, executive director of the Republican Party of Arkansas, sent her workers home early "out of an abundance of caution."
"Our hearts go out to everyone at the Democratic headquarters. What a tragedy," Ray said. "This is just a very upsetting, troubling and scary thing for our staff as well."
An impromptu vigil at University Hospital drew Gov. Mike Beebe and a number of state legislators who had worked with Gwatney.
House Majority Leader Steve Harrelson was at the state Capitol for a news conference on crime and that he didn't know of anyone who would want to harm Gwatney.
"You never think of something like this happening here in Arkansas," Harrelson said.
Sarah Lee, a sales clerk at a flower shop across street from the party headquarters, said that around noon Gwatney's secretary ran into the shop and asked someone to call 911.
Lee said the secretary told her the man had come into the party's office and asked to speak with Gwatney. When the secretary said she wouldn't allow him to meet with Gwatney, the man went into his office and shot him, Lee said.
FBI spokesman Steve Frazier said his agency was assisting in the investigation but could not offer any details.
Last November, a distraught man wearing what appeared to be a bomb walked into a Clinton campaign office in New Hampshire and demanded to speak to the candidate about access to mental health care. A hostage drama dragged on for nearly six hours until he peacefully surrendered.
The confrontation brought Clinton's campaign to a standstill just five weeks before the New Hampshire primary. Security for her was increased as a precaution. She said she did not know the suspect.
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