A 21-year-old White Oak woman, who allegedly had been assaulted Sunday afternoon by her ex-boyfriend, was stabbed to death early yesterday in her bedroom. Police found the bloodied ex-boyfriend sitting next to her bed and charged him with first-degree murder.

Montgomery County police said that on Sunday, Sheila T. Menefee and her 2-year-old son were trying to leave their apartment complex in the 1500 block of Heather Hollow Circle, behind the White Oak Shopping Center, when she was attacked by her ex-boyfriend, Ruben A. Diaz, 20. Her screams alerted neighbors, according to Capt. John Fitzgerald.

Officers arrested Diaz, and he was charged with second-degree assault. Fitzgerald said Menefee told the officers that she had been assaulted in the past but had been too intimidated to call police.

While Diaz was taken to the Montgomery County jail, Fitzgerald said, officers advised Menefee of steps she could take to protect herself.

"She heeded them," Fitzgerald said.

On the Sunday of a holiday weekend, Menefee persuaded the apartment building's management to change her locks. Later that afternoon, she went to a county court commissioner and obtained a protective order. Fitzgerald said the order was served on Diaz in the jail at 6:20 p.m.

"She did as much as she could do without physically moving," Fitzgerald said.

Less than three hours later, Diaz posted bond of $5,000 and was released. He could have paid as little as $500 to a bonding company to win his freedom, Fitzgerald said.

At 1:56 a.m., police got another call from Heather Hollow Circle. A woman told a dispatcher that her ex-boyfriend was banging on the door, Fitzgerald said.

Officers arrived at 2:03 a.m., knocked on Menefee's door and got no response. The rear sliding glass door had been smashed, possibly by a pole or piece of furniture, Fitzgerald said. The officers stormed inside.

Menefee's bedroom door was locked. Officers forced it open and found Menefee on the bed with multiple stab wounds, Fitzgerald said. Diaz was sitting on the floor, with a wound to his neck.

Menefee was taken to Holy Cross Hospital, where she died at 2:42 a.m., Fitzgerald said.

Diaz was taken to a trauma center outside Montgomery, where he remains under guard, Fitzgerald said. He will be served with a warrant charging him with first-degree murder when he is released, Fitzgerald said.

Diaz is not the father of Menefee's son. The boy, who witnessed the Sunday afternoon assault on his mother, apparently was home when the slaying occurred but was in his room and did not see it, Fitzgerald said. He is now in his father's custody.

Menefee was the 13th homicide victim in Montgomery this year. The slaying occurred in the same neighborhood where a Montgomery officer shot and killed a man last month. Peter Ayompeuh Njang, 25, of Adelphi was killed by Officer Candice Marchone, who said Njang pulled a knife when she approached him in the 11400 block of Lockwood Drive. That case remains under investigation.