Lawyers for a Georgia death row inmate say the drug the state plans to use for his execution Tuesday risks violating his constitutional rights.

In a court filing Thursday, lawyers for Brian Keith Terrell say the state still doesn't know what caused clumps to appear in its compounded pentobarbital earlier this year. They say that means problems could arise again and cause serious harm to their client.

Terrell is scheduled to die Tuesday at 7 p.m. at the state prison in Jackson.

Terrell was on parole in June 1992 when he stole and forged checks belonging to a friend of his mother, 70-year-old John Watson. Prosecutors say Terrell was supposed to return the money but instead shot Watson multiple times and then severely beat him.