California state prisoners are killed at a rate double the national average, with sex offenders making up most of the victims, a new report finds.

Although male sex offenders make up just 15 percent of the prison population in the state, they account for nearly 30 percent of homicide victims, according to an Associated Press investigation of corrections records.

The AP examined records of 78 killings that had been recorded by corrections officials since 2007. It shows that despite the state’s decision a decade ago to create a special housing unit to protect vulnerable inmates, such as sex offenders, they made up 23 of the deaths.

Sometimes they were killed amongst the general population of the prison, and sometimes they were killed within those very special units. Because the units also house individuals trying to quit gangs, sometimes they lead to inmates creating their own gangs, and acting violently to vulnerable inmates such as sex offenders, authorities said according to the report.

However, prison officials say much of the blame lies with California’s move to overhaul the prisons to reduce crowding, which meant that in 2011, lower-level offenders were kept in county lockups, meaning sex offenders had to share the prisons with a higher percentage of violent gang members.

Currently, the state of California is struggling to meet the minimum prison population level set by the courts: 137.5 percent of designed capacity. Until California is able to get well below that, it is not likely to put a stop to violent crimes, according to a consulting firm quoted in the article.

A total of 162 prisoners in California have been killed between 2001 and 2012, which represents a rate of about 8 per 100,000 prisoners, which is double the national average over the same time period. That rate increased to 15 per 100,000 between 2012 and 2013.

Of 11 homicide cases that were closed in the first half of 2014, 10 of the victims were considered “sensitive-needs” in mates, and the AP found that eight of them were sex offenders.