As the case progressed, public opinion (which was initially sympathetic to them) started to turn against the law enforcement officials, and the day before the Department of Justice was due to present its arguments, it was announced that actually, they didn't need Apple's help after all, and that a third party had agreed to do the hacking for them. A week later the case was dissolved, and the FBI announced it had opened up the phone without Apple's help.
Apple has asked the FBI to tell it how this was done - on the principle that, if a security vulnerability was exploited, then this represents a danger to other iPhone owners and needs to be patched. But the FBI has so far refused. It's believed that an Israeli firm, Cellebrite, performed the hack, but this hasn't been confirmed either.
All of which is comforting for iPhone owners on the one hand - because Apple is so determined to protect their privacy that it will stare down the might of the US government - but worrying, because someone out there has evidently worked out how to bypass the security. However, there are significant reasons to believe that the method, whatever it was, would not work on later models of the iPhone. The iPhone 5s and later have superior security features and Apple has claimed that it wouldn't be able to break into them itself, even if wanted to.
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