Seventeen years after the fatal shooting of a security guard during a Muttontown armored car robbery, a Dix Hills businessman went on trial Monday in federal court in Central Islip for the guard's death and the murders of two other men.

Christian Tarantino is charged with participating in the robbery, which led to the death of guard Julius Baumgardt, and later ordering the murders of associates Louis Dorval and Vincent Garguilo because he thought Dorval and Garguilo would turn him in to the FBI.

Dorval's body was found stuffed in a toolbox floating in the Atlantic Ocean in 1994, two months after Baumgardt was killed. Garguilo, the brother-in-law of Twisted Sister lead singer Dee Snider, was fatally shot in Manhattan in 2003.

The case was the result of years of investigation by federal and Nassau investigators who interviewed hundreds of witnesses and used DNA evidence taken from hair samples and voice analysis to finally make an arrest in 2008.

During opening arguments Monday in federal court, Tarantino's attorney questioned the credibility of prosecution witnesses.

Attorney James Froccaro said one witness expected to be called by federal prosecutors pleaded guilty to taking part in Dorval's murder and dumping his body. Froccaro accused another witness of cooperating with authorities to avoid a life sentence in a separate case.

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In her opening arguments, Assistant U.S. Attorney Carrie Capwell said the first of the three slayings took place in 1994, after Dorval and Tarantino robbed an armed car in Muttontown.

During that robbery, Dorval shot and killed guard Baumgardt, court papers say. Tarantino ordered the killings of Dorval and Garguilo, a friend and business partner, because he suspected they were about to inform on him to the FBI, Capwell said.

Capwell and Froccaro each spoke for about 15 minutes before a panel that included four alternate jurors picked Monday. One of the initial jurors had failed to appear in court Monday; the other three were dismissed after telling District Judge Joanna Seybert they could not serve.

After Capwell addressed the jury, Froccaro ridiculed the prosecution's case. He said one expected witness, who faces life in prison for drug trafficking, "has made lying to the government . . . an art form."Capwell acknowledged that several prosecution witnesses would testify about their own criminal histories. But she said their testimony about the murders would be backed up by forensic evidence.