Concord, N.H. ? A teen-ager who pleaded innocent by reason of insanity in the stabbing deaths of two Dartmouth College professors plans to change his plea this week  apparently to guilty or no contest.

The Superior Court in Haverhill announced that Robert Tulloch would change his plea at a hearing on Thursday, a few hours before Tulloch’s alleged accomplice is to be sentenced.

The court did not say how Tulloch planned to plead. Neither prosecutors nor Tulloch’s lawyer would say.

But Tulloch’s only options under the law are to plead guilty or no contest, and the punishment is the same either way, said John Kissinger, a former assistant New Hampshire attorney general.

First-degree murder carries a mandatory life sentence.

Prosecutors say Tulloch, 18, and James Parker, 17, both of Chelsea, Vt., killed Half and Susanne Zantop in the couple’s home last year while posing as students conducting an environmental survey.

Authorities say the two went to four other homes in the months before the murders, planning to kill people and steal their ATM cards, but were turned away or found no one home.

Parker has pleaded guilty to reduced charges and had agreed to testify against Tulloch at his trial, which was set for April 22.

Last week, the Boston Herald reported that Tulloch had asked for a plea bargain in order to spare his family the pain of a trial.

The newspaper quoted an anonymous source as saying prosecutors rejected the request, offering only the mandatory life sentence.