CONCORD, N.H. – The Vermont teen-ager charged with stabbing two Dartmouth College professors to death plans to change his plea this week to guilty or no contest, The Associated Press learned Monday.

Robert Tulloch, whose current plea is innocent by reason of insanity, has only those options under New Hampshire law, said John Kissinger, a former assistant attorney general.

John Kacavas, another former state prosecutor, said a judge was unlikely to accept a no-contest plea.

“It just doesn’t accept responsibility the same way a guilty plea does,” Kacavas said.

Tulloch, 18, will change his plea at a hearing Thursday in Grafton County Superior Court in Haverhill. His alleged co-conspirator, James Parker, pleaded guilty to a reduced charge and is scheduled to be sentenced in the same court a few hours later.

Tulloch’s change of plea will cap 15 turbulent months in which he will go from being a top student and the senior class clown in tiny Chelsea, Vt., to murder suspect on the run, to prison inmate facing a mandatory life sentence without chance of parole.

Tulloch and Parker were caught three weeks after the deaths in New Castle, Ind., while hitchhiking to California.

Tulloch’s lawyer, Richard Guerriero, declined to comment. Attorney General Philip McLaughlin said only that the state had made no deal with Tulloch.

Last week, the Boston Herald reported that Tulloch, 18, had asked the state for a plea bargain to spare his family the pain of a trial. According to the newspaper’s anonymous source, prosecutors rejected the request, offering only life imprisonment without parole.

George Ostler, Michael and Diane Tulloch’s lawyer, wouldn’t comment Monday on why Tulloch would change his plea. Ostler said the family plans to attend Thursday’s hearing.

Respected and even beloved in the Dartmouth community, Half and Susanne Zantop, 62 and 55, respectively, were stabbed repeatedly in their off-campus home in Hanover on Jan. 27, 2001.

Speculation about the motive ran wild, including revenge, thrill-killing and neo-Nazism directed against the German-born couple.

Few details emerged until two months ago, when prosecutors said Tulloch and Parker, 17, who also lived in Chelsea, Vt., killed the Zantops while posing as students conducting an environmental survey.

They said the teens coldly plotted the murders for months, including ordering military knives over the Internet. They said the pair went to four other homes in the six months before the murders, planning to kill people and steal their ATM cards, but were turned away or found no one home.

In December, Parker pleaded guilty to reduced charges and agreed to testify against Tulloch. He is scheduled to be sentenced Thursday afternoon as an accomplice to second-degree murder in the death of Susanne Zantop. Prosecutors are recommending a sentence of 25 years to life.

Kissinger said Tulloch, whose trial was to start April 22, could be sentenced on the spot if the judge is satisfied that his new plea is “knowing, voluntary and intelligent.”

Kacavas said Tulloch’s change of heart speaks volumes about the state’s case.

“You can infer from this that Jim Parker and the [evidence] that the state probably disclosed probably did tremendous damage to Robert Tulloch’s insanity defense,” he said.

Beyond Parker’s testimony, prosecutors said physical evidence – including fingerprints on knife sheaths found at the home and bloody footprints – tied Tulloch and Parker to the scene. Knives found in Tulloch’s bedroom had traces of the couple’s blood on them, and Susanne’s blood was found in a car owned by Parker’s mother.

Kacavas said it is extraordinary for a person to plead guilty to first-degree murder except as part of a negotiated agreement. He said the only case he could recall was that of Gordon Perry, who pleaded guilty to the 1997 shooting death of Epsom police Officer Jeremy Charron. Perry avoided a possible death sentence.

Audrey and Robert McCollum, the Zantops’ neighbors, welcomed Monday’s news. Robert McCollum rushed to the Zantops’ house after an arriving dinner guest found their badly hacked bodies and ran to his home.

Prosecutors in February said the McCollums’ home was the last one targeted by Tulloch and Parker – the same day the Zantops were killed. The McCollums were not home.

“It doesn’t take away the ghastliness of it, or the tragedy of losing these wonderful people, but what it does offer is an ending of this nightmare,” Audrey McCollum said, sobbing.