In this photo taken Sept. 24, 2015, a No Trespassing sign, at right, is hung by the steel gate of a house allegedly owned by jailed Eileen Ontong in Ibabao village, Cordova township, Cebu province in central Philippines. Ontong, along with her husband Wilfredo, was arrested May 28, 2013, by agents of the National Bureau of Investigation in a raid at their house allegedly after engaging in a cybersex syndicate. Ap Images WASHINGTON (AP) — Child sex offenders are the largest category of inmates in U.S. military prisons, yet a full accounting of their crimes and how much time they're actually locked up for is shielded by an opaque system of justice, an Associated Press investigation has found.

Of the 1,233 inmates confined in the military's prison network, 61 percent were convicted of sex crimes, according to the latest available data, obtained through the federal open records law. Children were the victims in over half of those cases.

Since the beginning of this year alone, service members victimized children in 133 out of 301 sex crime convictions, with charges ranging from rape to distributing child pornography.

Child sex assaults in the military have received scant attention in Washington, where Congress and the Defense Department have focused largely on preventing and prosecuting adult-on-adult sex crimes.

Daniel E. DeSmit, a Marine Corps chief warrant officer, spent at least $36,000 viewing and producing child pornography over the span of six years. In emails examined by Navy criminal investigators, DeSmit described his preference for sex with prepubescent girls as "the best experience."

A military judge in January found DeSmit, 44, guilty of a litany of sex offenses and sentenced him to 144 years behind bars. But he'll serve just a fraction of that. In an undisclosed pretrial agreement, the Marine Corps slashed his prison term to 20 years.

When the AP asked for the investigative report into DeSmit's case, the Naval Criminal Investigative Service rejected the Freedom of Information Act request on privacy grounds. The report was released only after the AP appealed. In this photo taken Sept. 23, 2015, a folder containing the charge sheet and photos of suspect Eileen Ontong is shown at Cebu Provincial Detention and Rehabilitation Center Records Section in Cebu province in central Philippines. Ontong, along with her husband Wilfredo, was arrested May 28, 2013, by agents of the National Bureau of Investigation in a raid at their house in Ibabao Village, Cordova township, Cebu province in central Philippines, allegedly after engaging in a cybersex syndicate. Marine Chief Warrant Officer 4 Daniel E. DeSmit was the biggest single customer of Ontong’s operation, according to a U.S. official familiar with the case. AP Images

The military justice system operates independently of state and federal criminal courts. The U.S. Constitution mandates a presumption of openness in civilian courts — trials are open to the public, as are court filings, including motions and transcripts, with exceptions for documents that have been sealed.

Anyone can walk into a county or U.S. courthouse and ask to read a case file, on demand, without providing a reason. That openness is designed to provide accountability.

But visibility into military trials is minimal. Court records are released only after many Freedom of Information Act requests, appeals and fees, and often months of waiting. While military trials are technically "open," as are civilian trials, they take place on military bases, which are closed to the public.

"I can sit at my computer in New Haven and find out what was filed five minutes ago in a case in federal district court in Seattle," said Eugene Fidell, a former Coast Guard judge advocate who teaches military justice at Yale Law School.

"But to get copies of motions filed last week in a general court-martial at Fort Lewis would take months if not years, while the Freedom of Information Act wheels ground along."

People wave an American flag in front a of a US nuclear-powered super carrier. Reuters Under military law, children are defined as "any person who has not attained the age of 16 years." Victims aged 16 and 17 are counted as adults, which is consistent with age-of-consent laws in most states.

Asked why the biggest group of inmates is behind bars for sex crimes against kids, Defense Department officials said judges and juries view these crimes as intolerable and are more likely to impose harsher prison terms.

They also said military prosecutors pursue verdicts in cases their civilian counterparts would never take to court — and the confinement numbers reflect that commitment.

Air Force Col. Chuck Killion, director of the Air Force judiciary, said that since 2008 the Air Force has secured convictions in 199 out of 223 child sexual assault cases — an 89 percent rate.

"It's not as if there are child sex crimes being swept under the rug somewhere," Killion said. "We simply don't do that."

But the Defense Department does not make it easy for the public to learn about child sex cases. After DeSmit's conviction in January, the Marine Corps summed it up in two sentences.

"At a General Court-Martial at Okinawa, Japan, Chief Warrant Officer 4 D. E. DeSmit was convicted by a military judge alone of conspiracy to commit sexual assault and rape of children, aggravated sexual abuse of a child, sexual abuse of a child, and possession of child pornography.

This image, photographed in Washington, Tuesday, Nov. 17, 2015, shows the short summary in report released by the U.S. Marine Corps of the court-martial of Marine Chief Warrant Officer 4 Daniel E. DeSmit. AP Images The military judge sentenced the accused to 144 years of confinement, a reprimand, and dismissal," a summary of the court-martial released by the Marine Corps reads.

And that's all the service would have said publicly, had the AP not pressed for more information, including NCIS's 198-page investigation of the allegations against DeSmit.

The most significant detail missing from the Marine Corps' brief public summary was the pretrial agreement. DeSmit had struck a deal with the military, according to court records. He pleaded guilty to 18 counts, including conspiracy to commit rape of a child. His prison sentence was limited to 20 years, not 144 as the Marine Corps had publicly said.

And he will do even less time if he is eventually paroled. In the military justice system, DeSmit is eligible to be considered for release from prison after serving one-third of his term.

DeSmit is one of dozens of sex offenders who have benefited from pretrial deals, according to the AP's analysis of the summarized results of courts-martial released by the military services. Since the beginning of July alone, 31 soldiers, sailors and Marines were convicted of sex crimes against children. Twenty of those cases had pretrial agreements.