OAKLAND -- A man who was 17 when he shot and killed an Oakland man in a robbery in 2011 expressed deep regret Wednesday before being sentenced to 19 years to life in state prison.

"If I could, I would go back in time," said 20-year-old Jonathan Johnson, who pleaded guilty to second-degree murder for killing 42-year-old Antonio Torres. "There's not a day that goes by when I am not haunted by that fateful evening."

Authorities say Johnson was part of a teenage robbery crew that targeted people wearing necklaces. Torres, a gardener and father, was working in a disabled friend's yard in the Fruitvale neighborhood on May 20, 2011, when Johnson and three other teens attacked him for his gold chain and iPod. Torres was shot in the back by Johnson as he tried to flee his assailants.

Members of Torres' large, close-knit family shed tears in a Oakland courtroom Wednesday as they spoke about their loss. Torres was a hardworking, big-hearted and well-respected man, they said, one who would have likely forgiven Johnson for his crimes.

"Over a gold chain, you took my brother's life away," Maria Ruiz said. "I don't understand it.

"Really, you have no idea, the devastation, how painful it is."

Johnson was one of two teens prosecuted as adults in the case. He was facing life in prison without the possibility of parole before he took a plea deal. James Lee Allen, 19, struck his own deal and was sentenced last year to 12 years in prison. A third teen was prosecuted in juvenile court and is serving time in the California Youth Authority system for murder.

A fourth defendant, David Hall, who was 19 at the time of the killing, pleaded no contest to being an accessory to murder and will be sentenced May 30.

Johnson, of Oakland, said Wednesday that he hopes to learn from his mistakes, better himself and one day earn forgiveness from the Torres family.

Contact Malaika Fraley at 925-234-1684. Follow her at Twitter.com/malaikafraley.