PLAINFIELD, N.J. (AP) _ A man who held police at bay for 18 hours at his family's mansion was charged Thursday with murdering his mother-in-law before the siege began.

Mary Mason's body was found in the basement of her restored 1902 mansion Wednesday after the standoff, which ended when Mark Masters, 28, fired several shots at police and then shot himself in the chest, authorities said.

An autopsy showed Mrs. Mason, 74, was asphyxiated, Union County Prosecutor Andrew K. Ruotolo Jr. said.

Her hands were cut off and an ax was found nearby. Ruotolo said the autopsy confirmed that the hands were severed after the woman was strangled. The prosecutor said Mason told police he cut her hands off.

Masters remained hospitalized Thursday in satisfactory condition. Bail was set at $1 million. He also faces seven counts of aggravated assault and two weapons charges.

The standoff began Tuesday after Masters' wife, Minka, fled the house and called police. According to Ruotolo, she said her husband brandished a gun and told her that her mother was dead and that he feared he would be blamed.

The mansion was the setting for the 1989 horror-comedy movie ''Basket Case II.'' Mrs. Mason and her daughter Minka, both widows, bought the house in March 1990. Masters was hired as a handyman, and soon married Minka.

Other relatives said Masters didn't get along with them or with Mrs. Mason, who suffered from Alzheimer's disease.