A letter left by a man who shot three judges dead and injured three others before committing suicide in a local court office on Tuesday suggested his motive was revenge on the court.

Zhu Jun, 46, who went on a killing spree in Lingling district court in Yongzhou, said in the letter that in 2006, he went on trial in the court for disputes over property sales. He won the lawsuit, with the court asking the losing party to pay him 20,000 yuan (US$2,940) as compensation in eight months.

However, Zhu, believed that eight months was too long, and he added that the court also delayed other compensations that were due him. These circumstances made him angry and revengeful.

He said in the letter he came up with the idea of revenge and suicide gradually after he divorced his wife in 2003 and was diagnosed with late-stage cancer in 2006.

At around 7:30 am on Tuesday, Zhu, who was head of a security squad of the postal bureau in Lingling district, lied to one of his subordinates that he needed to get some of the department's guns examined by higher authorities, and took the three weapons.

At 10:05 am, he barged into an office on the fourth floor of the court building and started shooting a submachine gun and two pistols.

Three senior judges died immediately, and another judge and two clerks were injured, one of them critically, said a spokesman for the city's publicity department.

With court personnel rushing in, Zhu put a gun in his mouth and pulled the trigger, according to local authorities.

Zhu's victims were not involved in his property case, local police said.

Zhu, who had a son, divorced his wife three years ago. He lived with his parents, an initial police investigation showed.

Local police have been investigating three people suspected of dereliction of duty by breaking regulations of firearm management after Zhu broke into the court with weapons.

The incident alarmed courts nationwide, with many adopting more strict security measures to ensure safety.

Several courts in Beijing increased security procedures and police guards. Fengtai district court held an emergency meeting immediately after the shooting on Tuesday, and now people have to go through three rounds of security checks to get into the court.

In Chaoyang district court, five or six policemen are now stationed at the security door, and the checks are strict and detailed. Liquids, cameras, and computers are all banned in the court.

"All courts in Beijing have been very careful about security, not only to protect judges, but also to prevent litigants having conflicts. I don't think the case in Hunan is likely to happen in any court in Beijing", said a publicity official from the Chaoyang district court.