WISCASSET, Maine (AP) _ A man already facing the death penalty in Nebraska for killing two boys there was found guilty of murder Monday in the stabbing and strangling of an 11-year-old boy more than eight years ago in Portland.

John J. Joubert, 27, originally from Portland, was found guilty in the August 1982 killing of Richard Stetson.

Joubert sat expressionless and blinked as the jury's verdict was read after less than two hours of deliberations. No sentencing date was set.

Joubert already is scheduled to be executed in Nebraska's electric chair on Dec. 7 for murdering two boys, age 12 and 13, there in 1983. He had been an airman stationed at Offutt Air Force Base outside Omaha when those crimes took place.

Prosecutors had said Joubert would be returned to Nebraska to face the sentence there no matter what happened at his trial in Maine.

His lawyer, Liisa Hamilton, said she expects him to appeal the Maine verdict, and will seek to withdraw his guilty pleas in the Nebraska murders.

Assistant Attorney General Eric Wright, who prosecuted Joubert in Maine, said he would seek Maine's maximum life prison sentence for Joubert. Wright also explained why Maine sought to try a man already on death row in another state.

''I think people in this state need to understand that we wanted to do our best to make sure that if he ever got out from under his death sentence in Nebraska he'd have no place to go but Thomaston to die,'' said Wright, referring to a state prison.

Joubert's reaction to the verdict was, ''No comment.''

Before the jurors began deliberations, they were challenged by both the defense and the prosecution to carefully compare casts of Joubert's teeth to photos of bite marks on the victim's leg.

Wright said the casts match the tooth marks. Hamilton said they don't necessarily match, and said she was unconvinced the marks on Stetson's body were left by teeth.

But the marks proved pivotal in the jury's final decision, as did testimony from a journalist who interviewed Joubert after the killing, said forewoman Terry Blazek, of Waldoboro.

Blazek said jurors were unaware of Joubert's Nebraska convictions.

''Every single one of us had no idea about what happened in the other states,'' she said.

Because of pretrial publicity, Joubert's trial was moved from Portland to Wiscasset, a small coastal town about 30 miles to the north.

Prosecutors relied heavily on testimony from a journalist who wrote a book about Joubert and claimed that, during an interview about his crimes, Joubert did not deny he killed Stetson.

In his final address to the jury, Wright took issue with the defense attorney's attempts to link an alternative suspect to the crime, saying that there was no evidence to support that.

Wright also labeled as ''unreliable'' the testimony of Dr. Norman D. Sperber, a forensic dentist called by the defense who said it was unlikely Joubert's teeth left the marks. The prosecutor said Sperber's testimony was riddled with inconsistencies and contradictions.

Hamilton attacked the testimony of Mark Pettit, a television journalist who has interviewed Joubert for a book he wrote about the defendant and his crimes.

Pettit testified that when he asked Joubert if he killed Stetson, Joubert responded: ''I can't lie to you. I can't tell you I didn't do it.''

Hamilton questioned why Pettit failed to go to the police with that information.

''Why would he make that statement to a reporter, of all people?'' said Hamilton.