NORTON -- In the latest snafu in a murder case with a history of bizarre twists, a co-defendant who turned star witness against his friends will not plead guilty to manslaughter as originally agreed, his lawyer says.

Prosecutors lack the evidence to support the charge against Jason Weir, 21, one of three local men charged with killing an elderly Quincy woman in a plot to share in her estate, Franklin lawyer Edward J. McCormick III said Monday.

Instead, Weir, of Norton, may plead guilty next month in Dedham Superior Court to being an accessory after the fact, which will mean shorter jail time, McCormick said.

Weir was originally charged with murder, but agreed to testify against his friends, Thomas Lally and Anthony Calabro, both of Norton, in return for a 10-year prison term for manslaughter.

If Weir pleads guilty to being an accessory, it means he could get out of prison sooner because the lesser charge carries only a maximum prison term of seven years and Weir has already served four, McCormick said. The case against Weir is now under review by the district attorney's office.

Weir is scheduled for a possible change of plea on Sept. 15, McCormick said.

Weir was the star prosecution witness against Lally, 24, who was found guilty of first-degree murder in March. Lally, who blamed Weir for the murder, is now serving a life term in prison without parole.

In June, Anthony Calabro, 23, the victim's great nephew and heir, pleaded guilty to second-degree murder and is serving a life prison term with a chance of parole after 15 years.

During his plea hearing, Calabro, who stood to inherit half of his great-aunt's house and money, admitted to acting as a lookout outside the apartment while his two friends were inside with his great aunt.

At Lally's trial, Weir took the witness stand and said he watched in horror as Lally beat 84-year-old Marina Calabro to death with a frying pan in December 2001.

`` If you look at Mr. Weir's testimony on how this homicide occurred, and look at his testimony at the Lally trial, the facts do not rise to the level to warrant a conviction of manslaughter or a plea of manslaughter,'' McCormick said.

`` He didn't have prior knowledge. He didn't know this murder was going to take place,'' McCormick said.

McCormick presented his argument in court last week before Judge Judith Fabricant, the regional administrative judge of the court.

He said prosecutors will now go back to the grand jury to seek an indictment on the accessory charge. David Traub, a spokesman for Norfolk County District Attorney William R. Keating, declined to comment specifically on issues raised by McCormick.

However, the office released a statement.

`` The district attorney's office has reassigned this case to the chief of our homicide division for further review in light of issues raised by the regional administrative justice following her reading of the trial transcript of the testimony of Jason Weir,'' Traub said in the statement.

McCormick said it is not unusual for trial testimony to differ from evidence presented to a grand jury. A grand jury indictment is merely an allegation, he said.

`` The defendants did not testify before the grand jury,'' McCormick added.

There were no independent witnesses to the murder and Marina Calabro's death was initially ruled an accident by the state medical examiner's office.

The medical examiner's ruling was the first in the history of twists in the case, which began when Marina Calabro's body was discovered at the bottom of a stairway.

The case was reopened in October 2002 after Weir told a friend about how Calabro was murdered and how her death was made to look like an accident.

The friend, James Morel, went to police and then wore a secret recording device so investigators could tape Weir talking about the murder and cover-up.

The taped conversations were played at Lally's trial.

The tapes were later linked to the firing last month of Susan Corcoran, the prosecutor on the case. The tapes were given to the CBS show `` 48 Hours Mystery'' to copy for a planned segment on the murder.

Before that and before Lally went to trial, prosecutors discovered that a DNA sample taken from the victim did not match any of the defendants.

Officials later determined that the sample was contaminated by a technician at the state police laboratory, providing ammunition for defense attorneys to challenge evidence in the case.