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A letter from Sgt. Bowe Bergdahl of Hailey was obtained by the International Committee of the Red Cross and provided to the Bergdahl family.
It is unclear when the letter was written but the family believes it was a couple of months ago, according to an email sent from Bergdahl's father, Bob Bergdahl, to Dwight Murphy, spokesman for the Boise Valley POW/MIA.
"Our family is greatly relieved and encouraged by this letter, which gives us hope that Bowe is doing as well as can be expected under the circumstances," Bob and Jani Bergdahl wrote in a statement released Thursday by Col. Timothy Marsano of the Idaho National Guard. Marsano acts as the family's spokesman.
"He was scripted and redacted but he was no doubt alive and his faculties fully functioning as of two months ago," Bob Bergdahl wrote in the email.
Bowe Bergdahl, now 27, was captured in Afghanistan on June 30, 2009, only two months after he was deployed as a machine gunner. He is believed held by the Haqqani network, a Pakistani group aligned with the Taliban. A senior Haqqani official last December denied the group had Bergdahl, saying he was being held by a Taliban group.
Bergdahl was reported missing after failing to show up for roll call. Since his capture, the Taliban has released five videos in which Bergdahl called for an end to U.S. involvement in the war and called for the release of Afghan prisoners held by the U.S. Military officials in the United States dismissed the videos as propaganda.
Bergdahl's family thanked the Red Cross for its assistance during Bowe's nearly four years in captivity, and also thanked the many Idahoans and others who have supported efforts to free their son.
"We hope Bowe's captors will again consider his parents' plea to release him, but in the meantime, we ask that you please continue to keep him in good health and allow him to keep corresponding with us," the Bergdahl family wrote in its statement.
Murphy said there was no doubt of the letter's authenticity.
"They know it was from their son," said Murphy, who served in the U.S. Marine Corps from 1976 to 1982. "Bowe Bergdahl is alive and there is hope to bring him home."
Yellow ribbons continue to adorn trees and light poles in Hailey to call attention to Bergdahl's plight.
Several events are scheduled June 22 in Hailey to mark the fourth anniversary of Bergdahl's capture. The day will be capped off by a tree dedication in Hop Porter Park. Four trees -- one for each year of Bergdahl's time as a prisoner -- will be planted. There will also be a 5-kilometer race, speeches by Blaine County officials and musical entertainment.
The Boise Valley POW/MIA will ride motorcycles to the event. Bob Bergdahl is scheduled to join the group in Hailey and ride his son's motorcycle.
Separately, thousands of motorcyclists are expected to take part June 13 in a New Hampshire ride dedicated to Bergdahl.
The annual Freedom Ride organized by the Northeast POW/MIA Network calls attention to prisoners of war and service members missing in action. The group travels 13 miles from Gilford to Meredith, N.H.
The Associated Press contributed to this report.