Both men were serving life sentences without the possibility of parole at the prison about 60 miles southeast of Little Rock.
The guard uniforms the inmates put on are made in the prison.
Video surveillance shows the men put them on in the prison library after the 6 p.m. headcount and walked out of the prison during a shift change less than 20 minutes later, Tyler said.
Prison officials are investigating whether all policies and procedures were followed.
"Someone should have laid eyes on them. That's one of the things we're looking at: How exactly did they get out without someone challenging them?" Tyler said.
Grinder and Adams drove away in a maroon or burgundy colored, 4-door sedan that had been left for them. Officials realized the men were missing after coming up short during the 10 p.m. inmate headcount, Tyler said.
Grinder was convicted of capital murder in 2004, and Adams was convicted of capital murder in 1995. Both men have family in Arkansas and out of state.
"We think there's probably a pretty good chance that they are not in Arkansas," she said.
Corrections officials are trying to develop leads on where the men are and hoping someone will spot them. Anyone who sees the men should call the Arkansas state police or their local law enforcement, Tyler said.
On the Net: