WILMINGTON, Del. -- It's not much: a 162-quart cooler found empty, lidless, with a bullet hole in one side and bobbing in the Atlantic Ocean.

But it is the key to the case that has riveted this small, close-knit city with TV-movie, crime-of-passion elements: The prominent, married attorney named Thomas Capano who is charged with killing his one-time mistress, Anne Marie Fahey, a pretty, troubled woman who served as scheduling secretary to the state's governor.

"That cooler became what he always intended it to become -- Anne Marie Fahey's coffin," prosecutor Ferris Wharton said yesterday in his opening argument in Capano's trial.

"Thomas Capano had determined that if Anne Marie Fahey could not be manipulated to be with him, she would be with no one forever."

Before a crowded courtroom in which the victim's and the defendant's families sat on opposite sides like the Montagues and Capulets, lawyers began unleashing their evidence, theories and scenarios.

Despite a lack of much physical evidence, the prosecution is expected to present a strong case based on testimony by intimates of Capano. They say they will prove that Capano killed Fahey in a jealous rage on June 27, 1996, because she was trying to break up with him after a three-year affair.

Capano's attorneys, however, quickly set about attacking the evidence and witnesses. Defense attorney Joseph Oteri even dropped a surprise scenario: that Fahey was not murdered, but rather the victim of an "outrageous, horrible, tragic accident" that Capano tried to cover up. He later refused to elaborate.

The crowded courtroom is an apt setting for the trial: With both Capano, 49, and Fahey, who was 30, well known in the city, the case is a web of interconnections. In fact, one of the prosecution's most critical witnesses is Capano's brother, Gerry, who agreed to testify after police raided his house and discovered cocaine and guns. He is expected to testify that he helped Thomas throw a cooler containing a body off the side of hisboat about 60 miles off the New Jersey coast.

Her body has never been recovered.

But Oteri was quick to disparage Gerry Capano's credibility, noting his history of substance abuse -- "cocaine, LSD, you name it." "He has no definable job. He's a typical screwed-up rich kid. He's a poster boy for the Me Generation."

Oteri also introduced another defense strategy: Confabulation, a psychological phenomenon in which people fill in the blanks of incomplete memories.

"A drug user's mind has black holes," said Oteri, whose thick Boston accent, white mane of hair and flamboyant style contrast with the more even, by-the-book prosecutors.

The Capanos are a rich, entrenched family here. They took up several rows behind the defendant, who frequently turned to smile and chat with them. His wife, Kay, and young daughters sat through hours of lawyers describing not just Thomas Capano's affair with Fahey but also with Deborah MacIntyre, who prosecutors say bought the gun that Capano used to kill Fahey.

Capano quickly emerged as a suspect after Fahey disappeared in June 1996 and their affair was revealed. It was another year and a half, though, before investigators had enough evidence to arrest Capano, who's been in prison ever since.

Capano, who appeared sallow and gaunt at yesterday's hearing,is one of four sons whose father created the prosperous Louis J. Capano & Sons construction company. He is a former chief legal counsel to a previous governor and, most recently, the head of the bond department of a prominent law firm.

Fahey, whose family and friends filled several rows in the courthouse, came from a vastly different world. The youngest of six children, Fahey was 9 years old when her mother died and her father spiraled into "intense" alcoholism, her brother Brian Fahey testified yesterday.

As their father eventually stopped working, the family became impoverished, sometimes going without food, electricity, hot water or telephone service.

Anne Marie was often sent to live with relatives or friends, something that Brian Fahey suggested led to her problems with depression, anxiety, eating disorders and near obsessive neatness.

Fahey's anorexia and abuse of laxatives left the 5-foot-10 brunette a dangerous 117 pounds at one point.

While the Faheys have wide sympathy here as details of their harsh childhood have emerged since Anne Marie's death, Capano's attorneys indicated yesterday that they would not be treating them with any special gentleness. He suggested the family tried to capitalize on Fahey's death by filing a civil suit against Capano. And he questioned how, if they are as close a family as they claim, they didn't know about their sibling's three-year affair.

After saying he was not going to besmirch the victim's character, Oteri went on to tell jurors that Fahey continually accepted money, gifts and clothes from Capano.

"She was onto a good thing and used it, and more power to her," Oteri said bluntly.

The opening arguments began yesterday after two weeks of a sometimes contentious jury selection process. Prosecutors charged that Capano's lawyers were purposely excluding whites from the jury, prompting the defense to demand, unsuccessfully, a mistrial. In the end, 16 whites, three blacks and one Hispanic were chosen as jurors or alternates.

To seat the jury, lawyers questioned 259 citizens about their opinions of the highly publicized case, whether they could sentence someone to death and any relationships they might have with the nearly 400 people on a list of potential witnesses.

In this small city, many know at least one of the major figures in the case.

"Or, in my case, knows all of them," said Kevin Freel, whose O'Friel's Irish Pub is a popular downtown gathering place. Freel is a friend of Judge William Swain Lee and the Fahey family, and, he pointedly notes, a former friend of Capano.

Freel had hired each of Anne Marie's five siblings over the years to work at his bar and used to tease her that once she was 21, she would be next.

"Oh, no, I'm going to be the only one who doesn't work for you," he remembers her countering.

Instead, she got a job from Freel's brother, chief of staff to then U.S. Rep. Thomas Carper, after she boldly called him and demanded, "Fast Eddie, hire me!"

Fahey began working as Carper's receptionist in Washington in 1991, then moved back to Wilmington when he became governor and promoted her to his scheduling secretary in 1993.

It was in the governor's office that the attractive Fahey -- Freel used to tell her she looked like supermodel Elle McPherson -- caught Capano's eye.

He asked her out to lunch and they subsequently began an affair that they kept secret from all but a few friends. He bought her expensive presents and they dined out lavishly, usually in Philadelphia rather than in Wilmington, where both were well-known.

Fahey, friends said, enjoyed the attention and gifts, yet also was guilt-stricken and fearful that her family would find out. She begged Capano not to leave his wife for her but the couple eventually separated.

Fahey began seeing another man and tried to break off the Capano affair. In a series of e-mails and her diary, both of which were made public after her disappearance, their relationship emerges as sometimes tender, sometimes obsessive. She wrote in her diary that Capano was a "controlling, manipulative, jealous, insecure maniac," but told him in an e-mail the following month that he would "always own a special piece" of her heart.

He often expressed concern over her health -- "TAKE YOUR VITAMINS" -- and continued to profess his love for her, even as he carried on a long-running affair with another woman.

Their last exchange of e-mail is particularly poignant. She apologizes for being "such a doggy downer," saying she jTC sometimes gets overwhelmed by her eating disorder and the intensity of her therapy sessions. He responds that she doesn't have to apologize.

"I promise," he continues, "to make you laugh tonight at Panorama, to order calamari and to surprise you with something that will make you smile."

He showed up that night with a $400 outfit that Fahey had admired while shopping at Talbots with her sister but couldn't afford. The promised laughs and smiles, though, were nowhere in evidence at Ristorante Panorama in Philadelphia, their waitress, Jacqueline Dasak, testified yesterday.

Capano did all the ordering, she said, and there was no conversation as both picked at their $154 meal.

Fahey's therapist later told police that Fahey feared Capano and only would have agreed to go to dinner with him in order to break up with him.

Fahey was never seen again.