Mary Jean Wilcox went to work early June 29, 1998, punching in at her Alexandria office at 7:19 a.m. Within the next 36 minutes, she was stabbed and cut 101 times by a co-worker, Roy Greene Jr., in an attack so violent that several of her teeth were knocked out and the diamond in her ring was dislodged from its setting.

After Commonwealth's Attorney S. Randolph Sengel described in Alexandria Circuit Court yesterday how Wilcox desperately fought for her life that day, Greene, 50, stood up and admitted that he had killed the 44-year-old Annandale woman.

Greene, who had been charged with capital murder, pleaded guilty to the lesser charge of first-degree murder and thus avoided a possible death sentence. In return, he has agreed that he will tell detectives why he killed Wilcox. Sengel said he made the unusual agreement with Greene in part because Wilcox's family has been yearning for an explanation of her death.

"We need to know why it happened," Sue Wilcox, 51, the victim's sister, said after Greene's hearing. "We're just thankful he had the conscience to come forward and plead guilty and save us from a lengthy and painful trial."

Sengel said that if Greene's explanation is not consistent with evidence in the case, the plea agreement is off.

Police believe that Greene, who was also charged with robbery, took a small cash box containing less than $200 from a locked filing cabinet in the office that morning. But they don't know whether that was the catalyst for the vicious attack on Wilcox.

Sengel painted a horrific murder scene as he described the "violent struggle" at the Association of Alexandria Radiologists, where Wilcox handled a variety of administrative duties.

A courier who came to the billing and collection agency in the 2800 block of Duke Street at 7:55 a.m. found blood everywhere--in the kitchen, on the walls behind the copying machine and on a chair near Wilcox's body. She had stab wounds on her head, face, neck and chest in addition to skull fractures and broken fingers, Sengel said.

Greene, who performed clerical and computer work at the office in the evenings and was responsible for locking up and setting the alarm, became very emotional when he was questioned by police and left the Washington area several days later without picking up his paycheck, the prosecutor said.

A shoe print left in the blood led detectives to Greene's Reebok athletic shoe, which after testing was found to have DNA on it consistent with a blood stain found in Wilcox's purse, Sengel said.

Greene had fled by bus to Atlanta, where he lived in a shelter and was able to secure a job at a Pizza Hut by dropping the "e" at the end of his name, altering his Social Security number and omitting that he had worked at the Alexandria business, Sengel said.

Alexandria Detective Wayne Smith, knowing that Greene had a child and an estranged wife, decided to check computer records on child support enforcement. Smith spotted Greene's name with the different spelling and police traced the name to Atlanta and the Pizza Hut. On Aug. 3, at the moment an FBI agent arrived at the restaurant to speak to the manager, Greene walked in and was arrested, Sengel said. Since his arrest, he has not talked to detectives.

Greene could receive a maximum of life in prison when he is sentenced Jan. 31.

Wilcox, who was single, is described by family and friends as a woman devoted to her relatives, her 7-year-old cat, Molly, and her elderly neighbors in Annandale, whom she often helped with errands.

Sue Wilcox has had her sister's diamond, which was found at the crime scene, placed in a new setting, and she is wearing it in her sister's memory. Mary Wilcox had inherited the diamond from their grandmother, her sister said.

CAPTION: Mary Jean Wilcox was stabbed in her head and face.

CAPTION: Roy Greene Jr. was linked to the crime by a bloody shoe print.