Apple CEO Tim Cook speaks about phone encryption battle with FBI

SAN FRANCISCO (KGO) -- Apple CEO Tim Cook sat down with ABC News' David Muir for an exclusive one-on-one interview. Cook is facing increasing pressure to unlock an iPhone belonging to one of the San Bernardino shooters.

The Apple chief had a message for the victims' families. "They have our deepest sympathy," he said.

He said he knows victims' families in the San Bernardino massacre are angry. "What they've been through, no one should have to go through. Apple has cooperated with the FBI fully in this case," he said.

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But Apple refuses to help the FBI unlock the iPhone of Sayeed Farook. Authorities believed he used the phone to communicate with his wife and accomplice.

That phone could hold information on other plots of terrorists involved in the San Bernardino attack.

"If we knew a way to get the information on the phone that we haven't already given, if we knew a way to do this that would not expose hundreds of millions of other people to issues, we would obviously do it," Cook said.

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He said it's a matter of privacy and public safety. Apple would have to write new software to unlock the encrypted phone.

"We view as sort of the software equivalent of cancer. We think it's bad news to write, we would never write it, we have never written it," he said.

When asked if he has any concern that he could prevent a terrorist attack by breaking into the phone, Cook responded, "Some things are hard and some things are right and some things are both. This is one of those things."

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