The legal team for accused mass-shooter Dylann Roof has filed a legal challenge over whether the death penalty violates the constitution.

Roof's attorneys filed a 40 page motion arguing that capital punishment is unconstitutional because of a high rate of conviction errors and the arbitrary nature of sentencing.

They also say they would drop the challenge and Roof would plead guilty if prosecutors took the death penalty off the table.

Dylann Roof is accused of killing nine people in the mass shooting last year at a church in Charleston, South Carolina.