AUSTIN, Texas (AP) - Eleven Texas prisoners have been killed this year inside the state's prisons, the highest number in at least 15 years.
    
The Austin American Statesman reports Sunday that last year, just three inmates were killed and that this year's total is the highest since 1997, when 10 were killed.
    
Officials say the increase is puzzling since overall violence, as well as sexual assaults and the number of weapons found in prisons statewide, have all declined in 2012.
    
Investigations into individual cases have shown that the homicides appear to be random acts of spontaneous violence between cellmates with no apparent pattern.
    
Officials therefore aren't blaming the fact that more convicts are serving longer sentences or that there are staffing shortages at some facilities.