Oklahoma has the highest rate of prison homicides in the nation, with state inmates killed at a rate more than three times the national average, according to the latest figures from the Bureau of Justice Statistics.

The figures reviewed by The Associated Press as part of a months-long investigation show 39 homicides at Oklahoma prisons between 2001 and 2012, a rate of 14 per 100,000 inmates. The second highest rate is Maryland with 11 homicides per 100,000. The national average is 4 per 100,000.

Oklahoma prison officials provided details on 38 killings inside Oklahoma prisons from 2005 to 2014, and a review of those cases show 10 of the inmate victims were convicted of sex crimes.

State Corrections Department spokeswoman Terri Watkins said each inmate goes through a screening process when they enter the system to determine if factors such as criminal history or gang affiliation could make them potential targets. She said each of the state’s prisons has segregated housing for vulnerable inmates.