Tokyo (CNN) Wreckage from a Japanese F-35 stealth fighter that crashed into the Pacific almost a month ago has been recovered, Japan's defense minister said Tuesday, but the reason for the loss of one of the world's most advanced warplanes remains a mystery.

Pieces of the jet's flight recorder and cockpit canopy have been lifted from the ocean floor, Defense Minister Takeshi Iwaya told reporters in Tokyo.

He described the condition of the flight recorder as "terrible" and said the device's memory part was missing, leaving investigators still wondering how the US-designed jet crashed April 9.

The jet and its pilot, Maj. Akinori Hosomi, went missing while on a training mission from Misawa Air Base in northern Japan.

Hosomi, a 41-year-old with 3,200 hours of flight experience, was last heard from when he signaled to his squadron mates that he would have to abort the mission before his craft disappeared from radar.

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