They are brothers who lived under the same roof, yet in a sense they are strangers.

Amin Oweiss, 19, and Omar Oweiss, 22 -- privileged sons of an Egyptian-born physician whose work secured their prosperous life in Potomac -- grew distant as their parents' marriage fell apart a few years ago.

Then, on Aug. 15, 2001, their father, Zakaria M. Oweiss, allegedly crushed his wife's skull with a hard rubber mallet in a rage over her infidelity. Now the divide between the brothers is a chasm, as each has taken a side in their father's murder trial in Montgomery County. Omar Oweiss was the star witness for the prosecution, while Amin Oweiss, in an interview Friday, called his late mother a "tyrant" and his father "an angel," a man incapable of homicide. His brother, he said, could have been the killer.

In the courtroom, as Zakaria Oweiss, 58, listened from the defendant's chair, his attorney also sought to shift suspicion to Omar Oweiss -- a strategy that prosecutors said had exceeded the bounds of decency.

Brother against brother, father vs. son. Acrimony, adultery and violence shattered the Oweiss family, and now the broken pieces have been laid bare in Circuit Court. After two weeks of testimony and arguments in the case, jurors will reconvene tomorrow to deliberate on a verdict, to sift through the family wreckage for the truth about a killing.

As described in court by witnesses and lawyers, the brothers are very different.

Omar Oweiss, who declined to be interviewed for this story, was a feet-on-the-ground achiever, a young man who earned money as a tennis instructor and headed off to college, initially aspiring to be a physician like his father. He communicated well with both his parents and was especially close to his mother, Marianne Oweiss.

Amin Oweiss, a Gonzaga High School soccer player who worked part time delivering pizzas in the summer, was the rebellious brother. Impulsive and taciturn, he fought with his mother over curfews, school work and household rules. His father, tolerant of his younger son's growing pains, often took Amin Oweiss's side, triggering clashes with his wife over how to raise him.

On the day Marianne Oweiss, 49, was bludgeoned in the couple's brick, two-story home, Omar Oweiss was in the house, in the 9500 block of Kentsdale Drive. He testified that after he heard his mother scream for help, he ran downstairs and found her body, then saw his father pacing in the driveway, a heavy mallet in one hand. He said his father asked him to lie to police.

During cross-examination and in his closing argument Friday, defense attorney Peter Davis portrayed Omar Oweiss as a logical suspect in the slaying. Each son had a motive for murder, Davis said, because both were angry with Marianne Oweiss over her extramarital affairs, which hastened the family's ruin. In the months before her death, Davis said, both sons regularly spewed foul invectives at their mother. Amin Oweiss was not at home at the time of the killing -- but his older brother was.

"Did you kill your mother?" asked Davis.

"I don't think I could live a day if I had killed my mother," Omar Oweiss replied.

Omar Oweiss, a senior studying economics at the University of Maryland College Park, said his brother and other relatives are treating him coldly, apparently because he is helping prosecutors.

"Since August 15, I have been extremely isolated from family members," he testified. "A few of them have tried to reach out. But I'm really alone in this. Even my brother seemingly -- I don't want to say turns his back -- but has a difficult time talking to me."

Amin Oweiss, who family members said withdrew from the University of Maryland Baltimore County this year, did not testify in the trial, nor did his father. In an interview, he said he does not believe Zakaria Oweiss is capable of murder. "My father's an angel," he said. "We had a very good life. There's nothing we didn't have . . . and my mother wasn't happy with it."

He scoffed at Omar Oweiss's assertion that testifying against their father was painful. "I believe he's enjoying it," Amin Oweiss said, adding that he has not ruled out his brother as a suspect in the killing.

Prosecutors Katherine Winfree and Deborah Armstrong alleged that Zakaria Oweiss, a gynecologist who practiced at Columbia Hospital for Women in the District, killed his wife shortly after she returned from a vacation in Egypt because he learned that she had been having a romantic affair with a scuba-diving instructor there.

This much is undisputed:

The couple's marriage had been troubled for some time. About a year before the slaying, the two began sleeping in separate bedrooms and leading almost separate lives.

In the winter of 2000-01, for example, plans for a family vacation in Egypt were complicated by Amin Oweiss's decision not to go on the trip. His father, deciding that someone had to stay home with his son, then 17, also backed out.

After an angry family meeting, Omar Oweiss and his mother went ahead with the vacation, accompanied by Omar's then-girlfriend. In Egypt, Omar Oweiss and his girlfriend witnessed his mother's dalliance with an entertainer she met there. Omar Oweiss confronted her about the relationship and urged her to break it off, telling her that if she wanted to be romantically involved with someone other than her husband, she should end her marriage first.

But he knew from secretly reading her e-mail that she and the entertainer stayed in contact. And he said it upset him.

Davis sought to portray him as more than just upset.

"You were angry, were you not?" he asked in court.

"I was disappointed," said the son.

In spring 2001, Zakaria Oweiss learned of the affair. The couple agreed that Marianne Oweiss needed some time to herself before deciding what to do about her marriage. That May, with her husband's blessing, she traveled alone to Egypt, to learn Arabic and scuba diving. Her husband joined her in July -- and soon learned that she was having a new affair, with her diving instructor. Omar Oweiss testified that his mother and father had a violent confrontation that left Marianne Oweiss with two black eyes.

Zakaria Oweiss cut short his trip and came home, vowing to get a divorce. Marianne Oweiss returned home Aug. 14. Omar Oweiss said he drove her home from Dulles International Airport as she cried, then carried her luggage upstairs, warmed her dinner and kissed her goodnight. He said his brother, who was furious with his mother, had refused to go to the airport.

Prosecutors allege that Zakaria Oweiss left home the next morning in his red Volkswagen Jetta, ostensibly to see patients in Washington. Instead, he allegedly told his secretary to cancel his appointments. After parking some distance from his home, prosecutors allege, he sneaked into the house and ambushed his wife, striking her at least seven times on the back of the head with the mallet. They said the attack left him speckled with tiny drops of her blood.

In court, Omar Oweiss described seeing his father in the driveway, holding the mallet.

"I said, 'Dad.' He came up to me [and] I went up to him," the son said. "The first thing out of him was, 'She attacked me.' And I said: 'Shut up. I'm calling the police.' " He said his father told him to wait until he got rid of the mallet. Omar Oweiss said his father drove off in his wife's Jeep, and when he returned a short while later, the mallet was gone. It has not been found.

Omar Oweiss did not tell police about the mallet until eight days later. On the witness stand, he said he initially withheld that critical information because, at the time, he was instinctively protecting his father.

Davis, in the defense's closing argument, said that the blood on Zakaria Oweiss could have been inadvertently splattered on him by paramedics who examined Marianne Oweiss and then assisted her husband because he was short of breath.

Davis said that Omar Oweiss was angry with his mother, and reminded jurors that he was in the house when the slaying occurred and that he lied, at least by omission, to the police. "It's not a tactic to point the blame at Omar Oweiss in this case," Davis said. "It is our purpose. It is our evidence that Omar is responsible for his mother's death."

But Winfree dismissed the theory as a desperate last gasp by the patriarch of a family in ruins.

"Ladies and gentlemen, do not let him brand his son a liar," she told the jurors. "And do not let him brand his son a killer. It is time to let Zakaria Oweiss know that you are not fooled by this horrible, reprehensible defense."

Zakaria M. Oweiss, 58, is charged with murder in the bludgeoning of Marianne Oweiss, 49. He had confronted her

over her infidelity.