Why doesn't the United States government negotiate with terrorists and/or criminals?

Okay, I’m going to admit that I don’t know the actual policy on how the US deals with the demands of terrorists and criminals but in television shows and movies I’m watching Bones right now the official policy seems to be no negotiation. I understand the idea that once you give in to one demand, more people will expect you to give in to their demands and thus more crimes will occur.

With this in mind, why is there no flexibility? I would imagine that when people’s lives are on the line, zero negotiation can be deadly. So, why is this the best path to take when people’s lives are on the line?

If anyone knows for sure that this is not the official policy, please let me know and link me to a source if possible.