A Dorchester man will serve up to 20 years in state prison for shooting a 45-year-old woman as she enjoyed a night on the porch two summers ago, Suffolk County District Attorney Daniel F. Conley said.

A Suffolk Superior Court jury on Friday convicted DERRICK RICHARDSON (D.O.B. 12/23/89) of aggravated assault and battery with a dangerous weapon, unlawful possession of a firearm, unlawfully carrying a loaded firearm, and two counts of assault with a dangerous weapon.

Judge Frank Gaziano imposed the sentences recommended by Assistant District Attorney Dana Pierce, a former gang prosecutor now assigned to the DA’s Senior Trial Unit: 14 to 15 years in state prison for the shooting, 4 to 5 years for shooting at her, and five years probation for firing at but missing a second woman at the scene. Gaziano ordered those sentences to run consecutively; Richardson’s sentences on the gun offenses will be served concurrently with those prison terms.

“This verdict and these sentences take a dangerous gunman off the street and out of the community for a long time to come,” Conley said. “Franklin Field will be a safer place without him.”

During three days of testimony, Pierce proved that a friend of Richardson’s had been shot on the night of June 4 in the area of 1067 Blue Hill Ave. Richardson was on the scene, the evidence showed, and threatened retaliation.

Early on the morning of June 6, Pierce showed, Richardson traveled from Stratton Street to Floyd Street wearing a hooded sweatshirt and carrying a .45 caliber semiautomatic Hi-Point handgun.

At about 1:30 a.m., Boston Police officers in an unmarked car saw Richardson and recognized from their training that he was displaying the characteristics of an armed gunman – he had been clutching his right hip area, cinched the hood of his sweatshirt close around his face, and was holding something inside the pocket of his sweatshirt.

The officers exited their cruiser to stop Richardson, but he drew the firearm and fired seven times at a pair of women sitting on a porch on Floyd Street – just around the corner from where Richardson’s friend had been shot. One round hit one of the women and another penetrated the wall of a nearby house, lodging itself in a window frame just above a sleeping baby.

As the officers commanded him to drop his weapon, Richardson briefly ran at them before surrendering and lying down in the street. He was immediately taken into custody.

Jennifer Sears was the DA’s victim-witness advocate assigned to the case. Richardson was represented by attorney Paul Davenport.