"They are asking for a backdoor into the iPhone," Sewell's testimony states. "Building that software tool would not affect just one iPhone. It would weaken the security for all of them.... We can all agree this is not about access to just one iPhone."
Sewell's testimony also states that FBI Director James Comey has acknowledged that the FBI would likely use the precedent in other cases involving iPhones.
The Justice Department has argued that the request is limited in scope and is necessary because it has been unable to unlock the iPhone used by Syed Rizwan Farook, who, along with his wife, allegedly killed 14 people and injured nearly two dozen in a shooting rampage in December in San Bernardino, Calif.
"Maybe the phone holds the clue to finding more terrorists. Maybe it doesn’t. But we can't look the survivors in the eye, or ourselves in the mirror, if we don't follow this lead," FBI Director James Comey, who will also testify Tuesday, said in a column on the Lawfare Blog last week. In the same column, Comey said the case San Bernardino case "isn't about trying to set a precedent or send any kind of message."
But in testimony before the House Intelligence Committee last week, Comey suggested the case "will be instructive for other courts."
Manhattan District Attorney Cyrus Vance, who will also be testifying Tuesday, previously said his office has 175 phones it is unable to unlock -- and told Charlie Rose he would "absolutely" push forward for access to them if the government prevailed in the case.
Apple formally challenged the FBI's request last week. On Tuesday, Sewell will put several questions before lawmakers at the hearing.
"Do we want to put a limit on the technology that protects our data, and therefore our privacy and our safety, in the face of increasingly sophisticated cyber attacks? Should the FBI be allowed to stop Apple, or any company, from offering the American people the safest and most secure product it can make?
"Should the FBI have the right to compel a company to produce a product it doesn't already make, to the FBI’s exact specifications and for the FBI’s use?"
Read the full text of Sewell's opening statement.