Nor will public opinion be on the government's side in Brooklyn, with the U.S. seeking data from a drug dealer's phone instead of a terrorist's, he said.
The government risks locking in an unfavorable ruling from the Brooklyn magistrate if his findings are upheld on appeal to a higher court. Magistrate judges' rulings don't have value as precedent, but U.S. appeals court rulings do, Edgar said.
The two phones were different models and the tool which the FBI used to break into the California phone last month likely wouldn't work on the handset at the center of the Brooklyn case. Comey suggested on Thursday that the method used to access the California phone is only effective on the iPhone 5C and earlier models.
Since the Brooklyn handset runs an earlier version of Apple's mobile operating system -- iOS 7 -- it may be easier to hack the phone's software. However, mobile forensics companies advertise that they are able to break into iPhones which run earlier versions than iOS 8.4.
In the pivotal clash over privacy rights, the Brooklyn judge called a U.S. argument that the company is required to cooperate under a 1789 law called the All Writs Act "obnoxious to the law."
Apple spokeswoman Kristin Huguet didn't immediately respond to a request for comment on the government's appeal.
After helping prosecutors unlock at least 70 iPhones, Apple last year stopped cooperating and said the company would no longer serve as the government's helper. Apple Chief Executive Officer Tim Cook said in February that U.S. demands for iPhone access are a chilling attack on privacy. The government disagreed, saying Apple is more concerned about its marketing and brand identity than about the safety of the public.
The government has sought Apple's help because self-destruct features on newer iPhones wipe out data if prosecutors try "brute force" techniques to hack in. The contents of the drug dealer's phone were not backed up to remote cloud storage, leaving the physical device as the only source of data, the U.S. said.
The U.S. said on March 28 that it had successfully decrypted iPhone used by a man who with his wife carried out a December attack in San Bernardino in which 14 people were killed. That ended a standoff in California between Apple and the Justice Department there.
Apple has already conceded that it could get into the iPhone in the Brooklyn case within a matter of hours or minutes, a law enforcement official told reporters Friday.
In court papers, the Justice Department has said Apple had previously helped the government unlock phones of people accused of drugging and sexually abusing children, a defendant who was later convicted of selling drugs in Florida, and a child pornographer. In each instance, the government said it won an All Writs Act order and Apple readily complied. The company extracted the data in child sex abuse case "immediately," the U.S. said.
The hacking tool used in the San Bernardino case was tested to determine if it would work on other phone models, the official said. The Justice Department official declined to discuss the results of the tests.
The official also declined to discuss any details about talks the Justice Department has had with outside entities about hacking into the iPhone in the Brooklyn case.
The official also said it is "premature" to say whether the U.S. will disclose the hacking tool to Apple.
If there's a master strategy at work for the Justice Department, it might be that it's seeking to appeal and lose, Edgar said. Then, "they could go to Congress and get legislation" that would impose more requirements on companies to help with investigations, he said.
But that would be a "cynical" view, Edgar noted.