Beauty queen Ingrid Marie Rivera beat 29 rivals to become the island's 2008 Miss Universe contestant on Nov. 23.

Miss Puerto Rico Universe 2007 beauty pageant winner Ingrid Marie Rivera, from Dorado, reacts with tears during the post-contest news conference at the Center of Performing Arts in San Juan in this Nov. 23, 2007 file photo. Police investigating that someone put pepper spray on a Puerto Rican beauty contestant's clothing said they found no traces of the substance and will continue to probe into the matter to see if anyone lied to them. (Xinhua/Reuters Photo)

The 24-year-old was composed while appearing before cameras and judges throughout the competition. But once backstage, she had to strip off her clothes and apply ice bags to her face and body. She swelled and broke out in hives twice.

"We thought at first it was an allergic reaction, or maybe nerves," pageant spokesman Harold Rosario said. "But the second time, we knew it couldn't have been a coincidence."

On Friday, the Caribbean island's Forensic Sciences Institute said the gown and the brush for makeup, delivered to police four days after the pageant, contained no traces of capsicum, pepper spray's active ingredient.

"I guess she has a lot of explaining to do," police spokesman Stephen Alvarez said on Saturday.

Police Superintendent Pedro Toledo said he would investigate whether anyone provided false information to his detectives, which would be a felony.

Rivera has not given any statements to police investigators.

Magali Febles, the director of the beauty pageant, insisted that the sabotage took place and said she would ask authorities to test for other substances.

Someone also stole Rivera's bag containing her gowns, makeup and credit cards. And a bomb threat forced pageant officials to postpone the last day of competition on Thursday, said Febles.

Beauty competitions are popular and fierce in Puerto Rico, which has won the Miss Universe pageant five times.

Rivera, who won Miss World Caribbean in 2005, had been a target of controversy from the start of competition, as rivals complained she was too experienced and should be disqualified.