"Because of the similarity in all of the devices, I believe they're linked," Blaine County Sheriff Gene Ramsey told the Idaho Mountain Express in a story on Wednesday.
No injuries have been reported due to the bombs.
Authorities said the devices were made of plastic containers filled with ingredients intended to create a chemical reaction and build up pressure until the container explodes.
One bomb consisting of three bottles taped together was found April 24 in a mailbox at a rural residence north of Hailey. Five other bottle bombs were found last week floating in a pond in the Elkhorn Village area of Sun Valley.
Authorities said one of the bottle bombs found taped to two others in the mailbox detonated ineffectively. A bomb squad from Twin Falls Police Department rendered the other two harmless.
"The one went off prematurely, but the others were swelling and had to be neutralized before we could touch them," Ramsey said.
Of the five found floating in the pond, authorities said four had exploded and one malfunctioned.
Interim Sun Valley Police Chief Walt Femling said no motive has been determined.
Ramsey said the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives is not assisting the investigation. He said his office and Sun Valley police were sending evidence to the Idaho State Police crime lab in Meridian.
Ramsey said whoever is making the bottle bombs "appears to be practicing to fine-tune their devices."
"If they continue to perfect their devices, it will probably only make them more dangerous," he said. "And my fear is that if they don't stop they're either going to injure themselves or someone else."
He said filling the devices with shrapnel likely would increase any potential penalties if the maker is found.
"When you attach shrapnel to any device that's designed to explode, you're creating a potentially deadly weapon," the sheriff said.
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