Explainer: military sex assault, by the numbers

Across the U.S. military last year, service members filed more than 6,000 sexual assault reports. About 1 in 20 resulted in jail time for the perpetrator.

Last year, 6,131 service members reported a sexual assault.

But only about 317 service members were court-martialed and sentenced to confinement as a result of a reported sexual assault.

The dizzying details underlying that roughly 1-in-20 conviction-and-incarceration rate were buried in the latest annual military sexual assault report released May 1, which reveals how sexual assault complaints were handled by criminal investigators and commanders.

Of those 6,131 reported sexual assaults, about 1,471 were "restricted reports," meaning the victim stepped forward and reported the assault for the purposes of receiving counseling but declined to identify the attacker or participate in any criminal investigation.

Of the remaining 4,660 "unrestricted reports," about 135 were alleged sex assaults that occurred before the victim entered military service, placing the perpetrator beyond the reach of the criminal justice system.

Of the remaining 4,525 reported sexual assaults, military criminal justice agencies initiated investigations in 3,934 of those cases. The difference of 591 is due to the fact that in some cases, multiple victim reports are consolidated into a single investigation or a report was filed late in 2014 and the investigation did not begin until early 2015, a defense official said.

Comprehensively tracking the outcome for every report for an individual year is difficult because many investigations extend into the following year and are mixed into that year's data.

This year's report says the military completed investigations targeting 3,648 alleged perpetrators in 2014. Hundreds of investigations from 2014 remained open at the start of 2015.

Of those 3,648 investigations that were closed, lawyers determined that 528 cases were "unfounded" because they were "baseless," constituted a "non-sexual assault offense" or stemmed from "allegations misinterpreted by a third party," the Defense Department report said.

Of the remaining 3,120 investigations, 252 were dismissed because investigators were unable to identify the perpetrator.

An additional 231 cases were dropped because the alleged perpetrator was either a civilian or foreign national who was outside the military's legal jurisdiction.

In nine cases, the target of the investigation died; in three others, the accused perpetrator deserted the military, the report said.

Commanders ultimately received 2,625 cases to consider for court-martial or other legal action. But when those cases were reviewed, 628 were dismissed outright for reasons including: insufficient evidence to prosecute (323); victim declined to participate in the command investigation (248); a command-level legal review said the allegations were legally "unfounded" (48); or the statute of limitations expired (9).

Of the 1,997 accused perpetrators against whichwho commanders substantiated charges, 477 were downgraded to non-sexual assault-related offenses.

Of the 1,550 perpetrators against whom charges were substantiated, commanders decided not to prefer court-martial charges for 552, opting instead for nonjudicial punishment (318), administrative discharge (111) or other "adverse administrative actions" (123).

After commanders preferred court-martial charges against the remaining 998 service members, 273 never made it to trial because either the commander later decided to dismiss the charges (176) or because the accused perpetrator was discharged in lieu of a court-martial (97).

Some 137 court-martial charges remained pending at the end of fiscal 2014.

Of the 588 sexual assault cases that went to trial, 154 alleged perpetrators were acquitted of all charges.

Of the 434 alleged sexual assault perpetrators who were convicted, about 117 were sentenced to punishments other than prison confinement, which may have included punitive discharges, reduction in rank, fines, restrictions or hard labor.

In the final tally, that left 317 service members who were convicted on any sexual assault charge and received a sentence that included jail time.