"Turning" this type of "evidence" means giving testimony to implicate accomplices
[DOC] [TLE] Evidentiary value of an approvers testimony | Law Teacher [PAR] The definition of the approver has been lucidly put in the words of Sir ... [5] 
Therefore, corroboration of the evidence of an accomplice is essential [6] ... 
accomplice is credible but it must go a little further and implicate the accused.