Hadden Clark was convicted yesterday of second-degree murder in the 1986 disappearance of Michele Dorr, bringing to a close one of Montgomery County's most notorious missing child cases but leaving unsolved the mystery surrounding her whereabouts.

Michele hasn't been seen since she walked out of her father's Silver Spring home on a hot spring day in a pink-and-white polka-dot bathing suit headed for a turtle-shaped play pool in the back yard. Prosecutors and police, who have dug up tracts all along the East Coast searching for the 6-year-old's body, say only Clark knows what happened to Michele.

Michele's teary mother, Dee Dee Appleby, said of the verdict and the emotional three-week trial, "Sometimes you have to go to hell to find the devil."

Montgomery State's Attorney Douglas F. Gansler said he hoped, now, that Clark would have "the moral courage to come forward and tell us" where Michele is.

But Assistant State's Attorney James Trusty said he isn't counting on it.

"He had that secret when the trial began," Trusty said, "and he can have it for the rest of his life." The case is believed to be only the second successful murder prosecution in the state in which the body has not been found.

When Clark is sentenced tomorrow morning, he faces a maximum of a 30-year prison term that could run consecutive to the 40-year sentence he already is serving.

He was sentenced to 30 years for the 1992 slaying of Laura Houghteling, 23, who vanished from her Bethesda home. Clark led police to Houghteling's shallow grave off Interstate 270 and Old Georgetown Road in 1993, after he pleaded guilty to second-degree murder in her slaying. Clark, 47, also was sentenced in May to serve a 10-year consecutive prison term for a 1988 theft from a Bethesda family from whom he rented a room. Another 30-year term essentially would amount to life in prison for him.

Clark, who glared at police and others in the courtroom audience throughout the trial, stared straight ahead and barely moved as the forewoman announced "not guilty" of first-degree murder and "guilty" on a second-degree murder charge.

Jurors interviewed after the verdict said they were initially divided on whether Clark killed Michele Dorr. But after listing the evidence against him on a chalkboard, several jurors said, they decided that he intended to kill the child but that prosecutors had not proved that the slaying was premeditated.

Clark's prosecution was considered a tenuous and difficult case for the state, and it held so much emotion for police and prosecutors that Edward Tarney, the lead detective on the case for seven years, broke into tears when he heard about the verdict by phone. Assistant State's Attorney Debra Dwyer called the conviction "the proudest day of my professional career."

Gansler noted that the prosecution had no motive, no eyewitnesses and no body to prove that a crime had occurred.

Moreover, jurors did not know about Clark's previous murder conviction. Montgomery Circuit Court Judge Michael D. Mason ruled that it would be unduly prejudicial for the jury to consider.

Perhaps most damaging to the prosecution was that Michele's father, Carl Dorr, had confessed to police that he had killed his daughter. Prosecutors argued that Dorr, who was going through a nasty divorce from Michele's mother, became so distraught after Michele vanished in his care that he "snapped" under the police scrutiny and suffered a psychotic breakdown.

Dorr said he was "very satisfied" with the second-degree murder verdict, saying he had feared that the jury might acquit Clark altogether.

Much of the prosecution's case also relied on the credibility of prison informants who testified that Clark confessed to them that he'd come across Michele playing with dolls alone in his niece's bedroom and that he had slashed her across the chest and then slit her throat so fiercely that he nearly decapitated her.

Prosecutors argued that Michele had gone to the home of Clark's brother, who lived two doors down from her father, and had wandered inside looking for Clark's niece, who was her favorite playmate. Inmates testified that Clark told them he shoved her body into a duffel bag and carried it to his truck.

Jurors saw the floor of the bedroom where the inmates said Michele was killed. However, tests performed on blood found between the wooden floorboards showed that none of the seven samples that were tested matched DNA in Appleby's blood, which would have matched her daughter's.

Clark's attorneys noted that Clark's timecard showed he clocked in to work at Chevy Chase Country Club the afternoon on which Michele disappeared. They also argued that Carl Dorr had more motive and opportunity to make Michele vanish and that, without the testimony from untrustworthy prison "snitches," the state had no evidence tying Clark to a crime.

Several of the jurors, six of whom lingered to exchange hugs with Michele's family, said they considered seriously whether Dorr could have abducted and killed his child but decided that he had been thoroughly investigated and ruled out as a suspect for a reason.

"It was tough [to reach a verdict] because everything was circumstantial," said juror Lisa McDanald, 34, of Germantown. "We didn't have any hard evidence."

When the judge told jurors after they reached their verdict that Clark was already imprisoned for murder, "we felt we had made the right decision," said juror Brent Mott, 40, of Takoma Park. "That made us feel comfortable."