A woman cleaning a house in Tempe stumbled upon a teenager's improvised explosive device yesterday.

Joshua Prater, an 18-year-old senior at Marcos de Niza High School, told police yesterday that he built the device when he was 10 years old, and said he didn't know it was filled with explosive powder, according to court documents obtained by New Times.

The device was made out of an empty carbon-dioxide cartridge, with low-explosive powder, match heads, and fireworks inside, with a hobby fuse.

Tempe Police Sergeant Mike Pooley said police have determined it to be a "legitimate" IED.

Court documents state that the device "meets the definition" of an IED, as defined in state law.

The cleaning lady -- who actually dropped off the device at a Tempe fire station -- also found more materials in the house, which she took pictures of and turned over to police.

Neither police nor a prosecutor at Prater's initial court hearing mentioned any malicious intent by Prater, but the state's attorney said due to "recent events," the cleaning lady finding the device in Prater's bedroom is "not something that we can take lightly."

The judge noted that pre-trial services deemed Prater a "low risk" to society, but she agreed with the prosecutor about the "recent events," setting Prater's bond at $10,000.

Prater's facing a felony charge of possessing a prohibited weapon.

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