PITTSFIELD -- Four firearms and more than 400 rounds of ammunition.

No one disputes those items were found in Gerald V. Gaetani’s small apartment on Bradford Street. At issue is whether Gaetani was in legal possession of the weapons when police discovered them during a search for his son, Justin, on March 3, 2013.

The 63-year-old Gaetani’s Berkshire Superior Court trial on 15 firearms-related charges began Tuesday. Police say they found two semi-automatic rifles, two handguns and the ammunition in Gaetani’s apartment. The serial number on one of the handguns had been removed.

"The only question you’re going to have is whether this defendant possessed these items," Second Assistant District Attorney Robert W. Kinzer III told the jury in his opening argument.

"Not ownership," Kinzer said, "possession."

Kinzer told the jury to pay close attention to Superior Court Judge Mary Lou Rup’s instructions with regard to the legal definition of "possession." Kinzer said that definition consists of three elements: a defendant’s knowledge that the weapons were in the apartment; the defendant’s ability to execute control over them; and his intent to exercise control over them.

Under the theory of joint possession, Kinzer said, someone can legally possess an item if they don’t own it, if they are aware that the item is present.

In his opening argument, Gaetani’s attorney, Joshua Hochberg of Pittsfield, said the guns and ammunition found in the apartment had been "hidden" from his client. The prosecution needs to prove that Gaetani knew that those items were there, Hochberg said.

Pittsfield Police Officer David Kirchner testified that officers went to Gaetani’s apartment at the request of Dalton Police who were looking for his son. Kirchner said Gaetani let them into the apartment to look around. But Gaetani asked police to leave once Kirchner found the two semiautomatic rifles inside a bedroom closet.

"He kept yelling, ‘Get out of my apartment,’" Kirchner said.

Police placed Gaetani under arrest when it was determined he did not have a license to legally possess those weapons, Kirchner said.

Police then applied for a search warrant, and found the two handguns when they searched the apartment. One handgun was found in a plastic bag inside a duffel bag, while the other was found in a baby’s diaper pail, which were also in the closet. Officers found apartment occupancy papers for Gaetani inside a bedroom drawer.

Matthew Powers, the property manager for the New Amsterdam Apartments on Bradford Street, where Gaetani lives, later testified that the defendant was the only person legally allowed to live in that residence.

Hochberg briefly cross-examined Kirchner, but declined to question either Powers or the prosecution’s three other witnesses, Pittsfield Police Officer Sean Klink, Dalton Police Officer Jeffrey Powell, or State Police Firearms Examiner Edward Cochran. The prosecution rested following Powers’ testimony,

Powell testified that Dalton Police took Justin Gaetani into custody at the Shamrock Village Inn on Main Street the night Pittsfield Police went to his father’s apartment. They had been looking for the younger Gaetani in connection with a vandalism incident.

Justin Gaetani, 30, is currently serving a 5- to 8-year state prison sentence after being found guilty of 22 firearms-related charges following a Superior Court trial in April.

He is expected to testify for the defense when testimony in his father’s trial resumes this morning.