This photo released by the Salt Lake County Jail shows Kendra McKenzie Gill, who was arrested with three others on Saturday Aug. 3, 2013, after allegedly throwing homemade bombs from her car. Gill was recently crowned Miss Riverton, Utah. AP Photo/Salt Lake County Jail SALT LAKE CITY (AP) — Prosecutors filed charges of bomb possession Friday against a recently crowned Utah beauty pageant winner.

Kendra McKenzie Gill was arrested last weekend with three accomplices for what one described as a prank. All four face the same set of four felony charges, prosecutor Blake Nakamura said Friday.

The 18-year-olds were arrested Saturday after driving around neighborhoods and allegedly tossing plastic bottles filled with caustic chemicals at people they knew. Nobody was injured.

"We don't really understand a clear reason for their behavior," Nakamura said. "The reason we charged them is obviously, what they possessed was indeed explosives, and we're alleging they were throwing them near homes and at people, and therefore, had the potential to cause a great deal of harm."

Felony bomb possession is punishable by 1 to 15 years in prison.

Gill was crowned Miss Riverton, topping a slate of nine beauty contestants earlier this summer in the Salt Lake City suburb. She showed off years of piano training with a Scott Joplin number and took home a $2,000 scholarship.

Others charged Friday were John Patrick Reagh, Shanna Marie Smith and Bryce Christopher Stone.

All four are due to make their first court appearance together Aug. 26 in Salt Lake City. Each has been released on $50,000 bond. Nakamura said some or all of the teens had attorneys, but he didn't know the lawyers' names.

All four acknowledged they were tossing bombs powered by a toilet bowl cleaner reacting with aluminum foil on sidewalks, front yards or in streets "to scare some of their other friends," Unified Fire Authority investigator Steve Bowen said in a court affidavit filed Friday.

Stone reportedly told authorities it was a prank.

"They were throwing them at both property and people," Unified Fire Authority Capt. Clint Mecham told KUTV-TV earlier this week. "This goes well beyond a teenage prank."

A Riverton pageant official didn't immediately return calls Friday on Gill's prospects for moving up in beauty competitions, or whether her title will be revoked.

"That's a local matter," said Jean Hatch, a producer for the Miss Utah Scholarship Pageant, set for next June.

Hatch said she didn't know if Gill's legal troubles would disqualify her from statewide competition.