Attorneys for Jacob Ryan Evans brought up the issue at a Wednesday hearing.
A U.S. Supreme Court ruling doesn't allow any capital murder defendant under 18 to be executed or sentenced to life without parole. Those are the only two punishment options for a capital murder convict in Texas.
Prosecutors say a proposed state law would create a life sentence for capital murder convicts under age 18.
Evans has been jailed since his October arrest at home in Aledo, 20 miles west of Fort Worth. The judge set bail Wednesday at $750,000.
Evans can be heard in a 911 call giving chilling details of the crime.
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