If a country has institutionalized and legal slavery (13th amendment), by its very nature it cannot have free and fair trials (6th amendment). These are contradictory statements.

We know that a significant portion of many state-run labour forces in many states are made up of enslaved people, whether they're chain-gang road workers in Louisiana or conscripted to fight wildfires in California. Life sentences or long, harsh penalties are incentivized because it provides a state with free labour. Even when their labour is not being literally exploited as legal slavery, the US runs prison as a strictly punishment focused system, not a reform based system - the cruelty is the point.

In that environment, you fundamentally cannot have fair trials.