BOB HARWOOD WAS ON THE OFfensive. Marching from desk to desk in a basement classroom of Shaffer Hall, he passed out flyers condemning Rex Chao as morally unfit to be chairman of the conservative College Republicans club. The 30 members, there to elect new officers for the upcoming term at Johns Hopkins University in Baltimore, studied the accusations with disbelief. The Rex Chao they knew was a popular student and gifted violinist from an affluent Long Island family. But Harwood, 22, a senior from Bradford, R.I., charged that the 19-year-old sophomore, once his close friend, had "distributed illegal drugs," "participated in a gang rape" and "sexually assaulted another male, revealing his true sexuality."

"Everyone thought it was garbage," recalls Michael McEleney, a junior who attended the April 10 meeting. "Rex defended himself very eloquently, but everybody said, 'Rex, you don't have to answer any of this. We know it's not true.' " Unopposed, Chao was quickly elected. When the meeting broke up about 10:30 that Wednesday night, Harwood followed Chao and his girlfriend, sophomore Suzanne Hubbard, outside, catching up with the couple on a well-lit path near the busy Eisenhower Library.

According to witnesses, Hubbard stood between the two men, warding off Harwood as he extended his hand to her in greeting. When Chao and Hubbard turned to leave, Harwood slipped his hand into a duffel bag, drew out a .357 Magnum, took quick aim and shot Chao in the back of the head. The wounded student spun to the ground. Harwood stepped over him, steadied the gun and fired a second round into his chest. He then hurried to Chao's nearby dorm, where he told a security guard to call an ambulance for his "buddy," adding, "I want a lawyer."

The 4,800-member student body was dazed with grief. Never before had there been a shooting on the campus of grassy quads and stately redbrick buildings. The 120-year-old school, with its high academic standards, had always seemed a refuge from the violence that plagued other city neighborhoods. Adding to the horror was the fact that the shooter and victim were good students who had shared an uncommonly close relationship. "These might be the last two you'd expect this to happen to," says school spokesman Dennis O'Shea.

The mystery deepened when authorities found scores of provocative e-mail messages that had passed between the two young men. Written over a period of months, many were oddly Victorian in their formality. "While having fun," Chao wrote in December, "we once again revealed and expressed ourselves to deeper levels and found profound joy in our bond." People close to the case say the passage refers to a gambling trip the two took to Atlantic City.

Other notes were deeply personal and documented a troubled relationship. Chao told Harwood in December that he was "the older brother I never had.... As the cultivator of my moral awakening, you are the pivotal figure in my life." In January, Harwood lamented Chao's sudden emotional distance: "I've cried out for your assistance, presence and help.... You know I'm a private person, very much an introvert, and when finally I wish to talk, to be silenced by one's friend really hurts."

Yet, in a rambling e-mail soon after, Harwood insisted it was Chao who was anguished—largely, Harwood reasoned, because Chao was denying his own homosexuality. Both young men had girlfriends, and friends and family say neither was gay. Still, Harwood seemed fixated on Chao's sexuality and told Chao that "your superficial involvement with Sue is preventing you from contacting me." He concluded that "you pushed aside a true friend for one that can hide who you are and provide temporary and superficial comfort from your deeply hurt and disturbed state."

Chao's friends and family from affluent Port Washington, N.Y., describe a young man who was anything but disturbed. He was the only child of native Chinese parents—Rosetta Chao, a social worker for the learning disabled and the blind for more than 20 years, and Robert, a retired electronics engineer. "Rex was a very curious little boy," says Louise Friedman, 73, his godmother. "He had to know about everything—birds, coins, stamps, Presidents."

Educated in private schools, Chao attended Waldorf School in Garden City, N.Y., then prestigious Phillips Academy in Andover, Mass. Even at Johns Hopkins, where he was a political science major, Chao was seen by his peers as capable of pulling down high marks almost without effort. "He could go to a class and he wouldn't have to take precise notes," says Taj Bayless, 21, a senior. "He was just brilliant, no two ways about it."

Chao also devoted countless hours to his two passions: music and politics. He decided early on that he wanted to play violin, and he quickly excelled, performing at school, during summer music camps and in community orchestras. He appeared dozens of times at St. Stephen's Episcopal Church, where his father is a lay minister. "When Rex played, people came to hear beautiful music," says Rev. Kurt von Roeschlaub.

A staunch Republican, Chao worked part-time this past academic year in the Washington office of Rep. Susan Molinari, a New York City Republican. Aside from loving the "machinations" of politics, he adored the glitz, says James Mazzarella, a Molinari aide. "He was really awed by political celebrities, so he would carry a picture directory around with him that had all the House members and senators so he could get their autographs."

It was, in fact, as a freshman in the fall of 1994 that Chao signed up for the College Republicans at Hopkins and met the group's chairman, Robert Harwood Jr. Unlike Chao, Harwood grew up in a working-class family. He was the oldest of three children born to Robert J. Harwood Sr., 42, a church custodian in Westerly, R.I., and Heather, 41, a cafeteria worker who moved to Massachusetts after the couple split four years ago. Harwood attended public schools and was an academic standout, becoming valedictorian of his 1992 class at Chariho Regional High in Richmond, R.I.

Like Chao, Harwood loved music, playing organ and piano on his own and French horn in the junior high school band. "Around the house he played a lot of church music and a lot of patriotic songs," recalls Beverly Harwood, 65, his grandmother. As a young member of St. Vincent de Paul Roman Catholic Church in Bradford, "Bob couldn't wait until he could become an altar boy," Beverly says, adding that as a child he talked of becoming a priest.

Things seemed to come naturally to Rex Chao; for Bob Harwood, personal success came through hard work. At 14, he took a part-time job preparing and serving food at the Westerly Nursing Home. During his college years, he worked summers at local restaurants, then in a Rhode Island chemical plant as a lab assistant. Though earning a partial scholarship to Hopkins, he enrolled in a work-study program as an accounting clerk to make ends meet. "He wanted things out of life, and he knew you have to work to get them," says his mother. "He bought his own car when he was 16, and he paid for it. He never asked us for anything."

At Hopkins, where tuition alone is nearly $20,000 a year, some students were surprised to learn that Harwood came from such modest means. "Bob was always generous with his money," says Michael McEleney explaining that Harwood regularly picked up tabs for friends' drinks and meals. "He dressed well. I always thought he was well-off." Adds his mother, Heather: "It's probably hard to be from a modest background and be around people who could afford things."

To save money, Harwood finished his course work for a degree in chemistry a semester early and returned to Rhode Island in December to stay with his grandmother. "He was sleeping a lot," says Beverly. "I call it 'burned-out.' He'd never been like that." He talked about wanting to go into patent law, combining his interests in science and law. But he made no plans for graduate school, nor did he look for work. His parents were relieved when he joined his father for a vacation in Florida in February, and then a group of college buddies for spring break in Cancún, Mexico, in March. "It was the first vacation he's ever had," says his grandmother. "We were really happy that for once he was doing something for himself."

But e-mails sent before and after the Cancún trip suggest he was obsessed by his failing friendship with Chao. What seemed a relationship of mutual admiration and shared political views was first shaken last summer, when, say those close to the case, Harwood took Chao to Baltimore's porn district for his birthday and offered to find him a hooker—an offer Chao refused. In later e-mails, both ask to be forgiven for moral lapses, though the issues are unclear.

Chao began to distance himself from his big-brother figure in October, when he and Hubbard, a flute player, began dating. The two met at a party after performing Mahler's "Songs on the Death of Children" for the Hopkins Symphony. "There are lots of people who go out just to go out, but they became something special," says Anthony DeBella, 21, a violinist and party cohost. "Rex was happier around Sue."

Harwood, who spent New Year's with the Chao family, began making increasingly forceful pleas for Chao's attention. "There were incidents when Bob went berserk when he could not locate Rex," Robert Chao told News-day after the shooting. In an e-mail in late December, Harwood pleaded, "In the future, when/if I ask you to call, PLEASE call." Other e-mails show that Harwood was distraught when Chao was caught in Washington in a December snowstorm and was unable to meet him in Baltimore for lunch. Angry that Harwood made it an issue, Hubbard told him in an e-mail, "Bob, it's a lunch, not marriage.... You need to realize that there are other people in Rex's life besides you." Shortly after New Year's Eve, Chao refused to see Harwood, communicating only through computers and friends.

By mid-February, Chao had grown so annoyed with Harwood's frequent e-mails that he complained to Susan Boswell, dean of students. After a second complaint, Boswell says she spoke with Harwood: "Robert was very polite and said that he understood and that certainly if what he was doing was bothering Rex, he would stop." But the communications continued. And before an orchestra rehearsal in March, says DeBella, Chao told him, "I am being stalked."

Though Boswell learned from Chao that Harwood owned a gun, she says Chao did not feel threatened, and Harwood assured her that the gun (which he bought from his father) was kept in Rhode Island. Still, she asked him to inform her or security whenever he planned a trip to campus. On April 9, Harwood told Boswell he wanted to attend the Republicans club vote the next night. Chao did not object, and Boswell arranged for the three to meet April 11 to talk things over.

Harwood's frame of mind in the weeks before the College Republicans meeting will be a key issue in the case. Being held on murder and gun charges, he has been undergoing psychiatric evaluation as his attorneys prepare to argue that a mental disorder made him incapable of planning the murder. In the meantime, families of both young men are trying to understand how Harwood could have gunned down his friend. Even in the end, in an e-mail in which Harwood strikes out at Chao for using "manipulative guilt-trips," he craved Chao's acceptance: "I have a great deal of respect, admiration, and affection for you, and I would still love to continue the wonderful, virtuous, and spiritual friendship and brotherhood that bonds us so closely in spirit."