Police in Utah are questioning two men over killer booby traps - one of them a spiked boulder - rigged up along a popular trail.
Tripping a ground wire would have sent the 20lb boulder crashing into an unsuspecting hiker, authorities said. Another trap was designed to trip a passer-by into a bed of sharpened wooden stakes, police said.
Two men arrested over the weekend on suspicion of misdemeanour reckless endangerment said the traps were intended for wildlife, but investigators did not believe the story.
The suspects built a dead-wood shelter as a possible lure for hikers who could step inside only through the two booby-trapped entrances, Utah County sheriff's sergeant Spencer Cannon said. "This is a shelter put together by people, visited by people - anything that would be impacted by their device would have to be humans," Sgt Cannon said. "It took some time to build these traps. They took rope, heavy-duty fishing line, and they intended what the traps were going to do."
The structure was easy to see, Sgt Cannon said, but the booby traps could have been overlooked by everyone except a military-trained officer like James Schoeffler of the US Forest Service, trained in hazardous device detection.
Mr Schoeffler was on a routine patrol along Big Springs Trail last week when he noticed the trip wires. "A lot of people go up there after dark, as well," Sgt Cannon said. "We're very, very fortunate that it was Officer Schoeffler who found it."
Authorities said he disabled the traps after taking photos and video of the site.
The area is in Provo Canyon, a popular hiking spot a few miles from central Provo. Sgt Cannon said the traps were just half a mile from a busy trailhead.
Authorities said a tipster alerted them about comments on Facebook that mentioned the traps and the shelter. Detectives then tracked down the suspects, Sgt Cannon said.
Benjamin Rutkowski, 19, of Orem, and Kai Christensen, 21, of Provo, were charged in the Utah County Jail on Saturday and released on bail.