ROY, Utah (Reuters) - One of two Utah teenagers accused of plotting to set off a bomb at a school assembly was inspired by the 1999 Columbine massacre in Colorado and visited the high school there to interview its principal, authorities said in court papers released on Friday.

The revelations surfaced as the older of the two Roy High School students arrested on Wednesday, Dallin Morgan, 18, was charged by Weber County prosecutors with possession or use of a weapon of mass destruction.

Morgan posted $10,000 bail on Friday and was released from the Weber County jail, Utah State Courts spokeswoman Nancy Volmer said.

The 16-year-old boy arrested with him, Joshua Hoggan, remained held at a juvenile detention center, where he was booked on suspicion of conspiracy, Volmer said. It was unclear if he had been formally charged.

Police in Roy, 30 miles north of Salt Lake City, have said the two students were not found to have any explosives in their possession after they were pulled out of classes and arrested on Wednesday following a tip from another student.

But authorities said investigators had found evidence that the two youths had plotted to set off explosives during a school assembly and make their getaway in a stolen airplane.

Charging documents filed against Morgan said that he did "conspire to use a weapon of mass destruction."

The arrest affidavit said that one of the students, whose name was blacked out on the document, had told investigators he was fascinated by the Columbine High School shooting spree.

Two Columbine students, Eric Harris and Dylan Klebold, shot 12 classmates and a teacher to death before killing themselves on April 20, 1999, in what then ranked as the deadliest outburst of school gun violence in U.S. history. Harris and Klebold also set off makeshift bombs fashioned from propane canisters.

The accused Roy High School student said to have been inspired by the Columbine massacre also told investigators he had flown to Denver and paid a visit to Columbine High to interview the principal there.

"It was confirmed by Columbine principal Frank DeAngelis that (the unnamed student) arrived on December 12, 2011, at 11 a.m. to interview him about Columbine's mass killing," the affidavit said.

It also revealed that at least one of the two accused students sent text messages to a third pupil before their arrest. One of those messages said, "Dallin is in on it." Another said, "He wants revenge on the world, too."

Police have said the two accused students had planned to escape after attacking their school by commandeering a plane from nearby Ogden-Hinckley Airport, a general aviation airfield. They trained for that plan with the aid of a computer flight simulator, police said.

The text messages cited in the affidavit also pointed to the possibility of a plane being used.

"We ain't gonna crash it, we're just gonna kill and fly our way to a country that won't send us back to the U.S.," the affidavit quoted one of the students as writing in a text message.

Police have not disclosed the date that they suspect the two students were planning to strike.

(Writing by Alex Dobuzinskis; Editing by Steve Gorman and Cynthia Johnston)

[Flickr image via Fishbowl Collective, Creative Commons Licensed.]

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