Apparently, the request that FBI made to Apple was not of unlocking a particular iphone (specifically the one that belonged to Syed Farook who was one of the major suspects in the December 2015 San Bernardino shootings). Instead, FBI had requested apple to completely update to an IOS version which would give FBI the authority to access the encrypted user data which is present on the device.
This does not look like an unreasonable request. However, one must notice that FBI itself does not have its secrets contained even though, it is supposed to have high security. Hence, this could be a big problem for Apple. So certainly, Apple is not to be held liable for its decision.