DEDHAM -- Thomas Lally and Jason Weir each told a Dedham Superior Court jury they saw the other kill Marina Calabro, the 84-year-old great-aunt of their friend, Anthony Calabro, who also is alleged to have plotted her murder.

Now a jury of seven women and five men are deciding which of the Norton men to believe.

Only Lally, 24, is currently on trial for the murder.

Anthony Calabro will be tried for murder at a later date and Weir has plea-bargained with the state for a lesser charge in exchange for testimony against his former friends.

The jury in the Lally trial deliberated Wednesday for 3 1/2 hours without reaching a decision on his guilt or innocence. They will return to deliberate today.

If convicted, Lally faces a sentence of life in prison without parole.

In her closing argument, prosecutor Susan Corcoran reminded jurors of testimony that Lally watched television shows about forensics and boasted up to a year before the 2001 murder that he could kill the retired hairdresser and make it look like an accident.

`` Mr. Lally became so obsessed with killing Marina Calabro that on December 19, 2001, with premeditation and with extreme atrocity and cruelty, he did just that,'' Corcoran told the jury.

The prosecutor said medical and forensic evidence backed Weir's testimony that Lally hit the elderly woman repeatedly with a frying pan and a tea kettle before strangling and suffocating her in a struggle to the death in her Quincy apartment.

Corcoran said Weir was consistent in his testimony and before his arrest in police wiretap recordings made without his knowledge that his participation was limited to helping Lally clean up the murder scene.

Weir, the prosecution's star witness, testified against Lally after reaching an agreement to plead guilty to manslaughter in return for a 10-year prison sentence.

The murder was initially ruled an accident but the alleged plot was uncovered after a friend of Weir's reported to police information he had learned about the killing.

Corcoran argued that Lally, in a police wiretap recording, never disputed Weir's statements and admitted after his arrest that he was not being truthful.

She said he was motivated by the easy money he was set to share when Anthony Calabro, an heir to his great-aunt's estate, received his inheritance. `` His plan went awry, ladies and gentlemen,'' Corcoran said.

But Lally's lawyer, Robert Griffin, attacked the police investigation, and called Weir a `` proud liar'' who boasted he could develop an alternate persona, beat a polygraph test and steal without getting caught.

Pointing to his client, Griffin said, `` Ladies and gentlemen, seated there is not the person who killed Marina Calabro. The person who killed Marina Calabro stood here, 5 feet away from you. That person was Jason Weir.''

He reminded the jury of police testimony that the crime scene on the night when Marina Calabro's death was reported was never secured, and that at least five officers trampled up and down the stairs where she was found.

He said the DNA evidence -- which the prosecution said did not exclude his client -- was botched, and told the jury they should not even consider it in their deliberations.

`` Ladies and gentlemen, the handling of the evidence in this case is nothing short of a disgrace,'' Griffin said.

The defense lawyer argued that none of the medical and forensic evidence supported Weir's testimony, saying the state medical examiner found no evidence of strangulation or suffocation.

Griffin said the prosecution failed to show any evidence that Lally `` received a nickel'' and reminded them about testimony that Calabro purchased $50,000 worth of musical equipment and related production costs for Weir's band, Electronic Kill Machine.

`` This was Jason Weir's rags to riches hope: that Electronic Kill Machine would take off and he would become a star,'' Griffin argued.

The jury has the testimony of 32 witnesses over seven days to consider, in addition to police wiretap recordings, more than two dozen crime scene and autopsy photographs and numerous documents.