HOUSTON (AP) The mother of infamous Branch Davidian leader David Koresh was stabbed to death and her sister was in custody Saturday charged with her slaying, authorities said.

An investigation into the death of Bonnie Clark Haldeman, 64, of Chandler, continues.

She was found Friday afternoon at the home of her sister, Beverly Clark, 54, in a rural area near Chandler, about 175 miles north of Houston in East Texas, Henderson County Sheriff Ray Nutt said.

"It's still under investigation and we really don't know what the motive was or what caused this to happen," Nutt said Saturday.

The sheriff said someone made a 911 call summoning deputies to the home Friday.

Clark was being held without bond in the county jail in Athens pending a court appearance. Jail officials said she did not yet have an attorney.

Authorities said Clark and her sister were the only two people in the house when deputies arrived. Authorities found a knife they believe to have been used in the slaying, he said.

The Athens Daily Review reported Saturday that Haldeman's body was taken to Dallas, about 80 miles to the east, for an autopsy.

Haldeman wrote an autobiography published in 2007 called "Memories of the Branch Davidians: The Autobiography of David Koresh's Mother," that described how her son, Vernon Howell, became David Koresh.

Agents from the U.S. Bureau of Alcohol, Tobacco and Firearms planned a surprise raid on the Koresh-led Branch Davidian compound near Waco on Feb. 28, 1993, trying to arrest him for stockpiling weapons and explosives. But gunfire immediately erupted, killing four agents and six members of the religious sect.

That led to a 51-day standoff, during which time 21 children and 14 adults left the compound unharmed. The complex caught fire and burned to the ground April 19, 1993, killing Koresh and nearly 80 of his followers, including about two dozen children.

The government claimed the Davidians committed suicide by setting the fire and shooting themselves. Survivors said the blaze was started by tear gas rounds fired into the compound by government tanks, and that agents shot them even those fleeing the burning building.

At the compound's remains on the 10-year anniversary of the February raid, Haldeman said it was unnecessary because her son would have surrendered if the local sheriff had served the arrest warrant.

"This was a harmless bunch of people," Haldeman said after attending the Waco service in 2003. "(A misperception) is that he was anti-government, collecting guns to kill people. That was an absolute falsehood. David didn't have a mean bone in his body. David did not believe in murder."

Associated Press Writers Anabelle Garay in Dallas and Angela K. Brown in Fort Worth contributed to this report.

Copyright 2009 The Associated Press.