Bill Gwatney was taken to hospital but died of his injuries
The chairman of the Arkansas Democratic Party has died after being shot by a gunman at the US state's party HQ.
Bill Gwatney, 49, was shot several times by a man who barged his way into his office near the state capitol building in Little Rock, police said.
The attacker was shot and killed after a police chase, officials said.
Democratic Party chairman Howard Dean said Mr Gwatney's killing was a "senseless tragedy". Bill and Hillary Clinton said they had lost a friend.
"We are deeply saddened by the news that Bill Gwatney has passed away," the Clintons said in a joint statement.
He was, they said, " a cherished friend and confidante".
The couple lived for years in the Arkansas capital of Little Rock while former President Bill Clinton was governor of the state.
Barack Obama, who competed with Hillary Clinton for the Democratic nomination to run for US president in November, also said he was "shocked and saddened" by news of the shooting.
Police have named the suspected gunman as 50-year-old Timothy Dale Johnson of Searcy, a town about 50 miles (80km) north-east of Little Rock, the Associated Press reported.
The motive for the shooting remains unclear.
A 17-year-old volunteer at the party headquarters building told AP that the suspect had pushed past staff to get into Mr Gwatney's office.
"He said he was interested in volunteering but that was obviously a lie," Sam Higginbotham said.
Mr Gwatney was taken to hospital in a critical condition and died of his injuries about four hours later.
He was a former state senator and was due to attend the Democratic Party's national convention in Denver later this month as a superdelegate.
He supported Mrs Clinton during the contest for the party's presidential nomination.
Last December, a man who claimed to have a bomb strapped to his chest walked into Mrs Clinton's campaign office in New Hampshire, prompting a hostage drama lasting several hours.