WASHINGTON — The young hacker was told in no uncertain terms: You are safe with me.

“I am not trying to find out your true identity,” AP journalist Norm Weatherill assured the teenager in an online chat. “As a member of the Press, I would rather not know who you are as writers are not allowed to reveal their sources.”

But Norm Weatherill was no reporter. He was FBI agent Norman Sanders Jr., and the whole conversation was a trap. Within hours, the 15-year-old hacker would be in handcuffs as police swarmed his house.

The 2007 bust would put an end to 10 days of nonstop bomb threats at the hacker’s high school but would also raise a troubling question that is unanswered to this day: How often do FBI agents impersonate members of the news media?

The answer is important, says one expert who played a key role in revealing the bureau’s subterfuge, because sources need to know journalists won’t turn them in.