The letters arrived in plain, unmarked 8 1/2-by-11 envelopes, with no return address.

And when newspaper editors and television producers across Utah examined the contents, they were perplexed.

“It was a complete surprise to me when I opened it,” said Joseph Cannon, editor of The Deseret News in Salt Lake City.

As an employee of a news organization, Mr. Cannon is accustomed to receiving a fair share of mail from the disgruntled and the outraged. And he assumed that the letter and its accompanying list, which purported to contain the names, addresses and phone numbers of illegal immigrants, was just another tasteless effort to grab his attention.

“My first impulse was to throw it away, actually,” Mr. Cannon said, adding: “It seemed like some sort of weird hoax. Who would do this?”