Brookfield, a town of 13,000 in scenic southwestern Connecticut, managed to reach its 193rd birthday without a recorded homicide. But the string snapped last Feb. 16. Shortly after 6 p.m. Arne Cheyenne Johnson, a 19-year-old tree surgeon, approached his landlord, Alan Bono, 40. As Johnson's fiancée, Debbie Glatzel, watched in uncomprehending horror, the young man repeatedly plunged a five-inch pocket knife into Bono's chest; the victim died an hour later of multiple wounds.

If the killing was shocking, so is Johnson's planned defense. When the State Superior Court convenes on Oct. 28 in nearby Danbury, Cheyenne plans to plead not guilty to the murder charge—by virtue of the fact that the devil made him do it.

More specifically, his attorney will argue that fiancée Debbie's youngest brother, David, was possessed by demons; that local Roman Catholic clergymen summoned to help had been unable to rid the boy of his hellish tormentors; that in an attempt to save the lad, Cheyenne had taunted the demons to enter him; and that, alas, the challenge was accepted, resulting in violence for which Johnson cannot be held responsible.

So far as Cheyenne's lawyer, Martin Minnella, 33, knows, demonic possession has never been advanced as a defense in the United States—but he cites its use in two British cases in the past 10 years. He claims an arson defendant was acquitted and an accused rapist received a suspended sentence. Understandably, the defense has its critics. Says Dr. M.B. Shimelman, assistant clinical professor of psychiatry at Yale, the patients he's seen who have claimed possession "were all schizophrenics. With proper treatment, the delusion went away." And Father Thomas Lynch, chancellor of the archdiocese of Hartford, Conn., holds that "99.99 percent of the people who claim they are possessed are not."

But Judy Glatzel, 45, wife of a heavy-machinery mechanic, is certain that David, youngest of her three sons, and Cheyenne, her prospective son-in-law, have literally lived through hell since July 3, 1980. That's when David, then 11, woke up sobbing and related how he'd been visited by an awful beast—"a man with big black eyes, a thin face with animal features and jagged teeth, pointed ears, horns and hoofs." The apparition warned him, "Beware." When David's visions persisted, sister Debbie, 27, asked boyfriend Johnson to move to the Glatzel home. "We believed David," explains Debbie. "He didn't lie, and he never liked anything spooky, not even scary comic books." The alarmed parents summoned a priest from St. Joseph's Catholic Church to bless their house—with no apparent results. By now David's beast was making daytime appearances too, in the form, he said, of "an old man with a white beard, dressed in a flannel shirt and jeans."

In desperation, the Glatzels called on a couple from nearby Monroe, Conn. who are self-styled "demonologists." Ed and Lorraine Warren, both 54, were professional artists until 1968, when they decided to pursue what was until then an avocation, the occult. Though they accept no fees for conducting demonic investigations, they lecture indefatigably (at up to $1,000 per), and once hosted a weekly local TV show, Ghost Hunting With Ed and Lorraine Warren.

Lorraine, who also claims the gift of clairvoyancy, describes her first encounter with David Glatzel: "While Ed interviewed the boy, I saw a black, misty form next to him, which told me we were dealing with something of a negative nature. Soon the child was complaining that invisible hands were choking him—and there were red marks on him. He said that he had the feeling of being hit."

Debbie adds that her brother began to miss classes. David also gained 60 pounds in the next few months, growled, hissed and spoke in strange voices, and would suddenly begin reciting passages from the Bible or from Milton's Paradise Lost. Every night a family member had to remain awake to monitor the youth, who would jerk into 30-minute frenzies of rapid sit-ups.

By now the Warrens were visiting regularly. "David made numerous references to murder and stabbings," says Lorraine. "We were sitting on a powder keg." The couple maintains that what they term "three lesser exorcisms" took place, the first at St. Joseph's with four priests in attendance. "We know there were 43 demons in the boy," says Ed. "We demanded names, and David gave us 43." But Father Nicholas Grieco of the diocese of Bridgeport, while conceding the Glatzel matter was investigated, denies any exorcism was performed. Yet the priests involved, who will not comment, were transferred to other parishes. In October the Warrens called Brookfield police and predicted tragedy.

Even as Cheyenne Johnson began to taunt whatever lay within David to enter his own body, Judy and Carl Glatzel sought psychiatric advice for their son. Last November the boy, termed by his family physician "normal" with a "minimal learning disability," was enrolled in a private school for disturbed children. But the house had become so unbearable that Debbie and Cheyenne moved out. She was hired by Alan Bono, who'd just moved to the community, as a dog groomer at the Brookfield Pet Motel; the couple was given an adjacent apartment.

But Cheyenne seamed changed. He'd never been in trouble with the law. Before dropping out of high school to help support his family, Cheyenne played Little League baseball, sang in the church choir and won awards as a newspaper carrier (one Christmas he used his earnings to buy his mother, Mary, 41, now a room inspector at a Bridgeport motel, an $80 jalopy so she needn't walk to work). But now Debbie feared that David's demons were possessing her audacious beau too: "Cheyenne would go into a trance. He would growl and say he saw the beast. Later he would have no memory of it. It was just like David."

Although a co-worker of Johnson's says that Cheyenne remained his usual polite self on the job, Debbie remembers four such trances in the six months before her fiancé killed Bono. Arrested two miles from the scene of the murder, Johnson has been held at the Bridgeport Correctional Center in lieu of $125,000 bail.

As the trial date looms, counsel Minnella is adamant about his client's plea. He has traveled to England to confer with lawyers who handled the two "possession" defenses, and Minnella has said he'll fly in exorcism specialists from Europe. He warns he will subpoena the priests involved if they don't come forward to testify. "I'm going to show the guy isn't insane and that it's not a delusion," he vows. "The courts have dealt with the existence of God, and now they'll be asked to deal with the existence of the demonic spirit."

Remote from such legal and philosophical questions is the unfortunate David, now a sixth grader. Once described as a smiling, open-faced boy, his expression is now clouded and grim, and he is still grossly overweight. His attacks are less frequent, but they have not entirely subsided, and he sleeps—when he can—with a light on. "I ask 'Why us?' and I still don't have the answer," says his mother. "But there is a God, and He will answer our prayers."