In the first Senate hearing on sexual assault in nearly a decade, Sen. Barbara Boxer (D-CA) slammed the military on Wednesday for its so-called "zero-tolerance policy," and called military sexual assault a "heinous, violent crime" and "we must stop it."

"Sexual assault is a heinous and violent crime and it must be treated as such. It isn't an internal matter. It is a violent crime and it must be treated as such," Boxer said.

Boxer, along with Texas Sen. John Cornyn (R), introduced an amendment to the National Defense Authorization Act that prohibited convicted sex offenders from joining the military.

"We know this crisis is staggering and despite some important reforms by the Department of Defense -- I thank them for those, they're trying to improve prevention, investigation, prosecution -- still too many military sex offenders go unpunished and too many victims do not get the justice that they deserve. As the chairman said, this is unacceptable and it must stop. And we are the ones who can stop it," Boxer continued.

Secretary of Defense Chuck Hagel recently ordered a review of sexual assault convictions that had been overturned by high-ranking officers.

"Immediate steps must be taken to prevent senior commanders from having the ability to unilaterally a decision or a sentence by a military court," Boxer said.

She spoke of two cases in particular: One in which Lt. Gen. Craig Franklin unilaterally overturned the conviction of Lt. Col. James Wilkerson, who had been stationed at Aviano Air Base in Italy, then recommended Wilkerson for a promotion, and another in which the Army decided to drop rape charges against Jeremy Goulet in Hawaii under a plea deal, then he went on to kill two police officers recently in California.

"What is it going to take to convince the military that sexual assault is a violent and vicious crime and that those who perpetuate it, they're capable of other violent crimes, including murder? What is it going to take? It is a vicious, violent crime and those that are capable of it are capable of other crimes. Yes, murder," Boxer continued.

"It is time for us to take swift, decisive steps to ensure that decisions in the military justice system don't rest solely in the hands of one individual," Boxer said. "It is not enough that our military says zero tolerance for sexual assault, you can say anything!"

The hearing was held by the Senate's Armed Services Subcommittee on Personnel and chaired by New York Sen. Kirsten Gillibrand (D), who said she was inspired by the Oscar-nominated documentary The Invisible War.

Coinciding with the hearing, Sen. Claire McCaskill (D-MO) introduced legislation that would block the ability of commanders to overturn sexual assault convictions and require written justification for any lessening of sentences given by military court.

Protect Our Defenders President Nancy Parrish said in a statement: "Our men and women in uniform have been incredibly encouraged by the leadership in the Senate from Sen. Claire McCaskill, Sen. Kirsten Gillibrand, Sen. Barbara Boxer and others for tackling the epidemic of sexual assault in the military. Officers convicted of sexual assault do not belong in our military. They should not be above the rule of law. If the Air Force is serious about addressing the ongoing epidemic of sexual assault then Lt. Col James Wilkerson and Lt. Gen. Craig Franklin should be removed from the Air Force."

Watch Boxer's testimony, published to YouTube on March 13.