CHICAGO — Adolfo Davis admits he was a swaggering thug by the age of 14 as he roamed and dealt drugs with a South Side gang.

He also describes a childhood of emotional and physical deprivation: a mother fixated on crack, an absent father, a grandmother’s overflowing and chaotic apartment.

From the age of 6 or 7, he often had to buy his own food or go hungry, so he collected cans, pumped gas for tips and shoplifted. At 10, he went to juvenile hall for wresting $3 worth of food stamps and 75 cents from a girl. At 12, he fell in with the Gangster Disciples.

“I loved them, they protected me, they were my family,” Mr. Davis said in a recent interview.

At 14, in 1990, he was out with two gang members when they robbed a rival drug house and shot the occupants, leaving two dead. Now 38, he has spent the last 24 years in prison on a mandatory sentence of life without parole.