"I am beginning to have grave misgivings about what I am doing, and what we are doing as a country," he wrote in the e-mail on Aug 5. "I no longer want to participate in the system, but I lack the courage to quit. I am married, with four children, and not only will they suffer, I'll lose a lot of friends."
Vandeveld has sparked criticism of the tribunals with claims that the government withheld evidence from detainees. But his correspondence with the priest and other statements suggest his defection was driven also by discomfort with the unforgiving treatment of detainees at the isolated U.S. Navy base in Cuba.
A 48-year-old veteran of the conflicts in Iraq and Afghanistan, Vandeveld has testified he went to Guantanamo in 2007 as a "true believer" in the Pentagon's specially designed system for prosecuting terror suspects.
He was assigned to lead the case against Mohammed Jawad, an Afghan accused of throwing a grenade that injured two American soldiers and their interpreter in Kabul in 2002. But he said the evidence he saw - some of which was withheld from defense attorneys - suggested the defendant was under 18 and may have been drugged before the attack. He saw other documents indicating Jawad was subjected to sleep-deprivation at Guantanamo.
In his e-mail to the priest, which was first reported by the Los Angeles Times, the Catholic said that while the detainees may be guilty, minimal thought was being given to their rehabilitation. He said he believed teaching tolerance would "end the hatred" of the Guantanamo prisoners.
Father John Dear, a Jesuit priest and social activist, encouraged Vandeveld to quit, telling him the U.S. operation at Guantanamo is "a sham."
"God does not want you to participate in any injustice, and GITMO is so bad, I hope and pray you will quietly, peacefully, prayerfully, just resign, and start your life over," Dear wrote in his e-mail.
The chief prosecutor at Guantanamo, Army Col. Lawrence Morris, said that Vandeveld never raised any concerns with him. He also denied that the government withholds evidence, saying his office goes beyond what the rules require in turning over material to defense lawyers.
Vandeveld quit in September, but he did not go quietly. Instead he reached out to his opponent in the Jawad case, defense attorney Air Force Maj. David Frakt, and provided a declaration and sworn testimony describing breakdowns in the system for providing evidence to detainees.
He is at least the fourth prosecutor to resign from the tribunals. Others have accused superiors of political meddling or deliberately misleading senior civilian Pentagon officials about the quality of evidence against defendants.
In his Sept. 26 testimony, Vandeveld said his change of heart was influenced by details of Jawad's story and his own evolving view of justice.
"I seek more restorative or reparative justice, rather than the rote application of the law," said Vandeveld, who resigned after his superiors rejected his recommendation to pursue a plea deal with a light sentence for Jawad.
He added that defense attorneys are unlikely to receive all the possible evidence in their cases because of disorganization in the prosecutors' office and the difficulty in obtaining documents from the military, the CIA, the FBI and other agencies.
"They have an impossible task of attempting to reconstruct six years after the fact all the evidence that has been collected in these cases," he said.
Jawad, who is now about 23, is expected to face trial in January on war crimes charges including attempted murder. He faces a maximum life sentence.