that's the whole point of the GJ.

usually prosecutors use the GJ process to secure indictments - they guide the GJ to find probable cause for trial by introducing only evidence that points toward probable cause and ultimately toward guilt. there's no judge present and no opposing counsel. usually only police officers who participating in the criminal investigation of the matter at hand testify. often the prosecutor will lead the witness through their testimony - the witness need only answer questions that suggest a yes/no answer. in almost all of the cases submitted to the GJ there is conflicting evidence and the prosecution only presents the evidence that points toward guilt. just like at most trials there's conflicting evidence - that's the point of a trial w/a fact-finder who sees/hears all evidence and later deliberates. normally defendants don't testify at the GJ b/c they are open to cross-examination on the record by the prosecutor w/o their lawyer present to advise them or object.

what the prosecutors did here isn't unusual for cases involving a police defendant. unfortunately. the prosecutors often don't want an indictment and submit the case to a GJ b/c they want to be able to point to an outside body that made the decision not to prosecute the police officer defendant. it's not unusual for a police defendant to testify at the GJ w/o being cross-examined. it's not unusual for other elements of the officers' defense at trial to be put before the GJ by the prosecution. prosecutor conduct at the GJ w/police defendants turns the whole process on its head (b/c the process relies on adversarial action by the parties and if there's no adverse action then the process doesn't really work), and it's standard practice.