With the network still reeling over the firing of one of its biggest stars, NBC News chairman Andy Lack acknowledged in a memo on Friday that the sexual misconduct allegations against Matt Lauer exposed organizational failures.

"Many of you have asked what we are doing to learn as much as we can about the circumstances around Matt Lauer's appalling behavior, why this was able to happen, and why it wasn't reported sooner," Lack said. "This week we saw that when an employee comes forward to report misconduct, the system works. The complaint is quickly assessed and meaningful action is taken. But we also learned that we must do a much better job of making people feel empowered to take that crucial first step of reporting bad behavior."

Lack also said that the network is taking steps to make it easier for women to come forward with complaints. He told employees that NBC's news division will implement an in-person sexual harassment training, to go along with the mandatory online training the organization already has in place, and that he is urging leaders to hold "smaller, more informal gatherings to further discuss this crucial issue now and on an ongoing basis."

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Lauer, the longtime co-host of the "Today" show and one of the highest paid anchors on television, was fired Wednesday morning after an employee at NBC filed a complaint about "inappropriate sexual behavior in the workplace." Since then, Variety and the New York Times each published allegations from more women against Lauer, who issued an apology on Thursday.

The memo on Friday came at a potentially precarious time for Lack as questions mount -- both in the halls of NBC and throughout the media world -- over what exactly was known about Lauer's behavior toward women. Variety, citing several unnamed women, reported that complaints to NBC executives about Lauer "fell on deaf ears given the lucrative advertising surrounding 'Today.'"

Immediately after the firing, Lack said this week represented the first complaint against Lauer in his career at NBC. After the Variety story published Wednesday afternoon, a spokesperson for NBC News said, "We can say unequivocally, that, prior to Monday night, current NBC News management was never made aware of any complaints about Matt Lauer's conduct."

An internal probe will likely determine the veracity of those claims, raising the potential for yet more fallout to come. Lack and other top NBC brass will be scrutinized as part of that effort.

In his memo on Friday, Lack said that a "team of the most experienced NBCUniversal Legal and Human Resources leaders have begun a thorough and timely review of what happened and what we can do to build a culture of greater transparency, openness and respect for each other.

"At the conclusion of the review we will share what we've learned, no matter how painful, and act on it," he said.