Locals in Gangwon Province found another North Korean unmanned aerial vehicle last October, months before the two drones that made headlines by crashing here recently.
But the Defense Ministry was only on Sunday alerted to the UAV that had crashed 940 m up a mountain in Samcheok, around 130 km south of the inter-Korean border.
Locals spotted it on Oct. 4 but only reported it to authorities after they saw news last week of the two other drones that crashed in Paju, Gyeonggi Province and on Baeknyeong Island.
The drone contained an outdated 486 processor and bore the number 35 painted on the body.
This suggests that the government and military were oblivious to infiltrations by North Korean drones for six months or more.
Authorities believe the drone found in Samcheok was on a surveillance mission over military installations along the east coast.
The military has now begun an intensive search for more crashed drones.