>Legal experts say his case is rare, even in Texas, the execution capital of America — and a state that allows capital punishment for people who did not kill anyone or did not intend to kill.

Forty six US states have Felony Murder statutes. I don't think this is all that rare for states with capital punishment. According to the wiki "...the death penalty may be imposed if the defendant is a major participant in the underlying felony and 'exhibits extreme indifference to human life'."