A Southbridge man will face charges of unlawfully carrying a loaded firearm after the Massachusetts Appeals Court found Boston Police officers were justified in conducting the pat frisk that led to its recovery, Suffolk County District Attorney Daniel F. Conley said today.

Prosecutors assigned to Conley’s Appeals Division last year challenged a Boston Municipal Court judge’s ruling that two plainclothes officers didn’t have a reasonable apprehension of danger when they became outnumbered in a South End alley while investigating a possible drug transaction. That ruling would have made it impossible to prosecute ENRIQUE CABRERA (D.O.B. 12/8/82), in whose pocket the gun was found on the night of Oct. 15, 2007.

Yesterday’s decision, authored by Justice Joseph A. Grasso, Jr., reverses that ruling, brings the gun back into evidence, and sets the stage for Cabrera’s prosecution in the Suffolk County Gun Priority Disposition Sessions, more commonly known as Gun Court.

“In sum,” the Court wrote, “when the facts and inferences underlying the officers’ suspicions are viewed in their totality, they constitute more than a hunch; they add up to reasonable suspicion.”

Conley hailed the decision.

“The officers involved were experienced enough to recognize potential criminal activity,” Conley said. “Their investigation led them into an alley where they were suddenly outnumbered. The Appeals Court acknowledged that the officers acted reasonably, appropriately, and safely when they called for backup and frisked the defendant.”

The Appeals Court found that the plainclothes officers had a reasonable suspicion of criminal activity when they followed a Virginia rental car and a Southbridge Volkswagen from the Back Bay MBTA station to an alley near 365 Massachusetts Ave., watched one occupant from each vehicle enter the rear of the building, and observed three other men exit the vehicles, leaving the Volkswagen still running.

“The number of participants, the use of a rental vehicle with out-of-State plates, and the measures taken to avoid detection reasonably suggested that the five individuals were engaged not in an isolated, hand-to-hand street level sale, but a drug deal of more than inconsequential magnitude,” the Court wrote. “Indeed, the facts known to the officers reasonably supported the conclusion that it was highly unlikely that five individuals in vehicles registered outside the locale, would meet in Boston to conclude a drug transaction unless the deal were of such a magnitude as to justify the time and expense.”

As the officers entered the alley and addressed the men, one of them produced a phone and surreptitiously began to enter a number. Shortly thereafter, Cabrera and another man exited the building. They appeared so nervous upon seeing the officers that they bumped into each other and attempted unsuccessfully to re-enter the building. The officers, with only one way out of the alley and confronted by a group of men who appeared anxious and may have been involved in the drug trade, ordered each man in the alley to place his hands on a car while they awaited backup.

“The officers found themselves outnumbered five to two, at night, and in a dead-end alley,” the Court continued. “They knew nothing of the defendant or the other individuals, or whether any other participants might remain inside the building. In such a rapidly developing circumstance, it was neither imprudent nor constitutionally unreasonable for the police to view the whole as greater than the sum of its parts and conclude that sufficient danger existed to merit a patfrisk and that backup was required to do so safely.”

Assistant District Attorney Elisabeth Kosterlitz argued the appeal. Cabrera was represented by attorney Patricia A. DeJuneas.