 Despite ratification of the Clause , compulsory process was not originally interpreted to permit co @-@ defendants to testify for each other . States relied on a fear that two defendants would both " swear the other [ out ] " of the charge to prevent either defendant from being convicted . In Benson v. United States ( 1892 ) , the Supreme Court explained the underlying common law theory for this prohibition ; namely , that only witnesses who were " unaffected as a party by the result , and free from any of the temptations of interest " could testify . Federal courts accepted these common law rules and expressly applied them in United States v. Reid ( 1852 ) . In Reid , the Court held that the common law pertaining to criminal procedure in force at the time of the Constitution 's ratification would be applied in federal courts ; this effectively kept the bar on co @-@ defendant testimony . While Reid was overruled on different grounds in 1918 , it stated the general practice for co @-@ defendants as witnesses that existed before the Fourteenth Amendment . 
