Charleston Church Shooter accepts life in prison plea bargain to avoid death penalty trial

So why would Dylan Roof want to avoid the death penalty?  Could it be that he preferred life in prison to the death penalty?  Could it be that the threat of the death penalty is something that the killers fear more than life in prison?  How much money also did this plea bargain save?  A trial like that would have been costly.  From the Washington Post:
Dylann Storm Roof, the high school drop out and white supremacist who shot and killed nine black parishioners at a historic Charleston church in 2015, pleaded guilty Monday to state charges stemming from the massacre as part of a deal with prosecutors to spend the rest of his life in prison to avoid a second death-penalty trial. . . .