“I find it hard to believe that someone could have written a novel with all these twists and turns in a small rural county in Texas,” said Bruce Wood, the county’s top elected official. “People are relieved but still stunned.”

Image Kim Lene Williams, 46, was charged with capital murder, which means she could face the death penalty if convicted. Credit... Kaufman County Sheriff, via Associated Press

The two prosecutors that the authorities say the couple conspired to kill had helped convict Mr. Williams last year on burglary and theft charges in a dispute about three computer monitors worth less than $1,500. The Williamses — he a portly, diabetic lawyer who volunteered with the Texas State Guard; she his ailing yet supportive wife of 15 years — were accused of pulling off what even ruthless criminal organizations have rarely dared in modern times: the executions of two prosecutors, and the wife of one, to avenge a guilty verdict.

Mr. Williams was already being held at the Kaufman County jail on $3 million bond, accused of sending an anonymous e-mail threatening another attack, when law enforcement officials announced Wednesday that they had arrested his wife. She was charged with capital murder in connection with the slayings of the district attorney, Mike McLelland, 63; his wife, Cynthia McLelland, 65; and another prosecutor in Mr. McLelland’s office, Mark E. Hasse, 57.

Ms. Williams joined her husband at the jail about 3 a.m. on Wednesday and was in custody on a $10 million bond.

According to an affidavit filed by the authorities, Ms. Williams confessed to her involvement in the shootings in an interview with investigators on Tuesday, and told them that her husband had been the one who shot Mr. Hasse in January and Mr. McLelland and his wife in March.