A Washington state man shot and killed his five children, between the ages of seven and 16, then turned the gun on himself after his wife told him she was leaving him, in the third mass shooting since Friday in the United States.

James Harrison, 34, killed his children early Saturday inside his mobile home in Graham, 100 kilometers (65 miles) south of Seattle, then drove to a nearby casino and shot himself inside his car, a Pierce County sheriff?s spokesman told reporters.

Ed Troyer said Harrison on Friday looked for his missing wife and found her at a convenience store with another man. The woman said she was leaving Harrison to be with her new boyfriend.

Alerted by neighbors, police found the five children dead, some shot several times, inside the mobile home's bedrooms and one inside the bathroom. Harrison was found dead with a rifle shot to the head, inside his car, with the engine still running.

"This is our theory of what happened," Troyer said. "We're still working to lock down everybody's account of what happened and when.

The family tragedy marks the latest spasm of gun violence in the United States which has been rocked by six fatal mass shootings in the past three weeks, including three cops killed Saturday by a 23-year-old man at his home in Pittsburgh, Pennsylvania.

The Pittsburgh attack came a day after a recently unemployed man stormed an immigrant services center where he had been learning English in Binghamton, New York and went on a murderous rampage, killing 13 people before taking his own life.

On March 29, a heavily armed gunman shot dead eight people at a North Carolina nursing home, days after six people were killed in an apparent murder-suicide in an upscale neighborhood in northern California's Silicon Valley.'

And on March 10, an unemployed man killed his mother, grandmother and eight others on a vicious shooting rampage in Alabama.

Criminologist Jack Levin, of Northeastern University in Boston, Massachusetts, said there appears to be a link between the failing US economy and rising body count.

"A mass killer is someone who has almost always suffered a catastrophic loss -- that's the link between a recession and mass killings," he said, citing the loss of a job, the loss of a lot of money or the loss of a relationship.

"Catastrophic losses serve as inspiration, or precipitant," he told AFP.