The FBI has told local law enforcement agencies that it will provide technical assistance to unlock iPhones in criminal cases around the US when permitted by law.
In the letter to local law enforcement, the FBI said that it understood the challenges of suspected criminals "going dark" -- a metaphor the FBI has repeatedly used to describe its inability to read messages and tap communications.

"As has been our longstanding policy, the FBI will of course consider any tool that might be helpful to our partners. Please know that we will continue to do everything we can to help you consistent with our legal and policy constraints," the letter obtained by BuzzFeed reads, which was later shared with other news outlets.
The letter was sent just days after the government formally dropped its legal action against Apple, which refused to rewrite software that CEO Tim Cook said would "undeniably create a backdoor" for every modern iPhone and iPad.

The government found an "outside party," thought to be (but never formally confirmed) as Israeli security firm Cellebrite, which was able to bypass the security features embedded in the iPhone used by one of the San Bernardino shooters.
Days later, the FBI agreed to help an Arkansas prosecutor unlock an iPhone using the newfound solution.
The FBI has not said what the unlocking method was, or if it will tell Apple as part of its responsible security vulnerability disclosure policies.

If they had proper strong encryption FBI couldn't unlock shit.