SAN FRANCISCO — For weeks, the United States government has said that the only way to open an iPhone used by a gunman in a mass shooting was to get Apple’s help, a position that set off a clash between the technology giant and law enforcement.
But remarks by a federal prosecutor in a court conference call on Monday and a letter from the F.B.I. director, James B. Comey Jr., published on Wednesday indicated a recent flurry of activity behind the scenes between law enforcement and other parties that have suggested methods to break into the phone.
Mr. Comey, in a letter to The Wall Street Journal, wrote that the case between Apple and law enforcement over opening the iPhone has stimulated people worldwide to try to get into the device.
And in a court transcript of a conference call on Monday with Apple’s lawyers and Sheri N. Pym, the federal magistrate judge presiding over the case, a Justice Department attorney, Tracy Wilkinson, said, “There have been a lot of people who have reached out to us during this litigation with proposed alternate methods.”
The comments offer a window into the action that law enforcement agents have seen in the five weeks since the case first erupted with a court order demanding that Apple help unlock the iPhone used by Syed Rizwan Farook, a gunman in the San Bernardino, Calif., rampage last year. While the government’s court filings have painted a picture of agents who had run through all possibilities in opening the device, it appears that since the case became public, they have been presented with more options than publicly indicated.
Those options were partly the result of how atypical this case has become. The unusual prominence of the fight between Apple and the government — it brought the sometimes abstract debate over privacy and security mainstream — generated the cascade of behind-the-scenes approaches by third parties to law enforcement over potential ways to open the iPhone.
“The F.B.I. and D.O.J. often pursue these kinds of cases under seal, and the public doesn’t know about them at all,” said Andrew Crocker, a lawyer with the Electronic Frontier Foundation, a digital rights organization. Mr. Crocker said the “public nature” of this case allowed more people to be involved.
On Monday, the Justice Department said a third party had offered a potential solution for breaking into the iPhone without wiping the data from the device. That led to a postponement of a court hearing in the matter and a reduction of hostilities between Apple and the government.
It is unclear if the third-party method will succeed in opening the device; the government said it would present a status report on any progress by April 5. If law enforcement cannot open the phone with help from the third party, the Justice Department may still ask the court to decide whether or not to require Apple to help investigators break into the gadget.
The Justice Department declined to comment. The agency is not legally obligated to reveal that it has been fielding more potential solutions for opening the phone.
Apple said it declined to speculate on the F.B.I.’s methods and actions. The Silicon Valley company has previously expressed doubts that the government could find no way to break into its iPhone, even as it constantly updates its security protocols.
“Given the past exploits that have bypassed the lock screen and the present-day reality of innumerable security firms, malicious actors, cybercriminals and potential adversaries of the United States constantly seeking vulnerabilities,” it seems improbable for the government to conclude that the only way into the phone was for Apple to write new code and weaken its security, Erik Neuenschwander, the company’s manager of user privacy said in a recent court filing.
The F.B.I. has tried many ways to get into the iPhone used by Mr. Farook, such as exploiting a previous bug that allowed unsigned code to be loaded and run on the device, Stacey Perino, an electronics engineer with the F.B.I. has said in a court filing in the case.
The F.B.I. also tried tools made by the agency and a mobile forensics company, Cellebrite, which let older iPhones load and run code that could crack a device passcode, Ms. Perino wrote. Cellebrite describes itself on its website as a subsidiary of Sun Corporation, a publicly traded Japanese company; it has done work for a number of government agencies.
Yet none of those tools worked, Ms. Perino wrote in the court document that was filed March 10.
Christopher M. Allen, a spokesman for the F.B.I., said the agency could not comment on the identity of the outside party.
Mr. Crocker of the Electronic Frontier Foundation said having to run through additional viable options had slowed government efforts to compel Apple to weaken its security functions.
“In having to consider these third-party solutions, I think the D.O.J. has been given a small taste of its own medicine,” Mr. Crocker said.