WORCESTER - Jury selection got underway Wednesday for the Worcester Superior Court trial of an 82-year-old Salisbury man charged with murder and robbery in the shooting death of an armored truck guard during a 1991 holdup at a Lincoln Street supermarket.

Ralph DeMasi was indicted in 2016 on charges of first-degree murder and armed robbery in the May 18, 1991, killing of Edward P. Morlock Sr., 52, of Athol in the foyer of the Shaw's supermarket at 490 Lincoln St. Mr. Morlock, who worked for Massachusetts Transportation Inc. of Marlboro, was gunned down as he carried bags of money from the store, according to authorities.

Mr. Morlock was not scheduled to work that day, but had agreed to take the shift of a fellow employee who was celebrating his birthday.

Prosecutors allege that Mr. DeMasi was among five men who took part in the robbery and was one of the gunmen who opened fire on Mr. Morlock, who died after being shot multiple times. Three of the alleged participants in the robbery have since died, according to prosecutors.

Mr. DeMasi has denied the allegations against him and pleaded not guilty.

He was indicted, authorities said, after new evidence was uncovered during an investigation into the 1991 robbery and shooting by the Worcester Police Department Unresolved Homicide Unit, the FBI and state police. The indictments were handed up three years after Mr. DeMasi completed a 21-year federal prison sentence for his role in an attempted armored truck robbery in Newburyport in September 1991.

Among those expected to testify against Mr. DeMasi is Ronald Martel, formerly of Worcester, who has said he was the getaway driver in the 1991 robbery and has been granted immunity, according to court records.

Also on the list of potential witnesses is Police Chief Steven M. Sargent. As a young patrolman in 1991, he was among the first officers to arrive at the crime scene and was at the hospital to speak to Mr. Morlock when he was pronounced dead.

It is expected that the trial will include about five days of testimony, which will begin Monday.

Sixteen jurors, including four alternates, will be seated. The lawyers in the case are being allowed to question prospective jurors during the selection process, which is expected to take two days.

Assistant District Attorneys Terry J. McLaughlin, Brett F. Dillon and Ellyn H. Lazar are prosecuting the case. The prosecution is proceeding under three separate theories of first-degree murder: that the killing of Mr. Morlock was premeditated, that it was committed with extreme atrocity or cruelty and that it occurred during the commission of a felony, armed robbery, that carries up to a life sentence.

Mr. DeMasi is represented by lawyers Michael S. Hussey and Paul Rudof.

Judge Janet Kenton-Walker is presiding over the trial.