A divided Supreme Court on Thursday dismissed Alabama’s bid to be allowed to execute a convicted murder who was found by lower courts to be intellectually disabled.

The court’s action leaves in place lower court rulings in favor of Joseph Clifton Smith, 55, who has been on death row roughly half his life after his conviction for beating a man to death in 1997.

The Supreme Court prohibited execution of intellectually disabled people in a landmark ruling in 2002. The justices, in cases in 2014 and 2017, held that states should consider other evidence of disability in borderline cases because of the margin of error in IQ tests.

The issue in Smith’s case is what happens when a person has multiple IQ scores that are slightly above 70, which has been widely accepted as a marker of intellectual disability. Smith’s five IQ tests produced scores ranging from 72 to 78. Smith had been placed in learning-disabled classes and dropped out of school after seventh grade, his lawyers said. At the time of the crime, he performed math at a kindergarten level, spelled at a third-grade level and read at a fourth-grade level.

The justices had taken up the case to consider how courts should handle such borderline cases of intellectual disability. Arguments took place in December.

Rather than issue a decision, though, the high court dismissed the appeal, an unusuaI action that leaves the last lower-court ruling in place.