The leaders weren't interested in truth; they were interested in their own power. When evidence is ignored, what agenda is really at play?
The question the leaders asked – 'What shall we do to these men?' – wasn't a question of justice, but of political expediency. They weren't concerned with what was right, but what was practical for maintaining their authority.
As one commentator noted, they abandoned their role as a court of justice to discuss 'what policy was most expedient.' They knew the miracle was real and that Peter and John acted with divine authority. Their fear wasn't that the apostles were wrong, but that the truth would spread and undermine their control. This is why their next step was not to investigate further, but to silence the witnesses.