PETERSBURG—Gang leader Kalvin B. Kelley was sentenced to 25 years in prison yesterday for conspiring to kill a city police detective and other crimes associated with his control of a Bloods-affiliated gang in the Tri-Cities area. Given the chance to apologize or offer any explanation for his actions, the 21-year-old Kelley chose to say nothing before Circuit Judge Pamela S. Baskervill pronounced the sentence.