Undated (AP) _ A list of mass slayings in a 15-day period in December:

Dec. 2 - A man killed a police officer and three workers in an unemployment office in Oxnard, Calif., apparently out of anger over his fight for unemployment coverage. He later was shot to death by police.

Dec. 7 - A gunman fired repeatedly as he walked through a Long Island Rail Road commuter train near New York City. Six people died and 17 were wounded. The suspect, black Jamaican immigrant Colin Ferguson, was driven by racial hatred, police said.

Dec. 14 - A man shot four workers to death and wounded a fifth at a pizza parlor in suburban Denver. Police arrested Nathan Jerard Dunlap, 19, who was fired from the restaurant four months ago.

Dec. 16 - Paul de Renne, 47, a geologist involved in a mining claim dispute with his brother Don de Renne, pulled a pistol in a Boise, Idaho, conference room. Police said de Renne killed his brother, another person and committed suicide.

Dec. 16 - A man killed a school superintendent and wounded a principal and teacher at a high school in Chelsea, Mich. Police arrested Steve Leith, 39, a chemistry teacher who was involved in a union grievance.

Dec. 17 - A man in Hugo, Okla., opened fire in a shopping center, killing two people before committing suicide.