NBC's top news executives asked "Today" co-host Matt Lauer about reports that he had sexually harassed colleagues, but Lauer repeatedly denied them in the two weeks before he was fired, according to people at the network.

The executives, including the chairman and president of NBC News, were tipped by NBC employees, who had received media inquiries about Lauer's alleged misconduct, according to a network executive. When the NBC managers confronted Lauer about the reports, he responded by saying he was "racking his brain and couldn't think of anything at all," said the executive, who was not authorized to speak for the record.

If the timeline is credible, it means that NBC News Chairman Andy Lack and President Noah Oppenheim were unaware of Lauer's alleged misconduct until very recently. The network has maintained that its management was "unequivocally" in the dark about Lauer, who reportedly harassed colleagues for more than 15 years.

Lauer, 59, was fired Wednesday, roughly 36 hours after NBC News received its first formal harassment complaint from a network employee. (At least two more women have subsequently come forward.) He became the latest in a long line of prominent men in the news media, politics and entertainment whose careers have crashed during the past two months because of accusations of sexually inappropriate behavior.

An NBC News source said Friday that Lauer will not be paid past his last day of work, effectively Tuesday, when Lack informed him he was fired. His $25-million-a-year contract, one of the most lucrative in the TV business, was supposed to run through the end of next year.

In the days before Lauer's dismissal, Lack and Oppenheim, as well as other senior managers, questioned him "multiple times, in multiple ways, [and] in multiple settings" about what had effectively become the office buzz, prompted by reporters from Variety and the New York Times.

The two publications had been contacting people at NBC News about Lauer but hadn't contacted NBC News's top executives at that point, the network executive said. NBC News announced Lauer's sacking on "Today," several hours before Variety and the Times published their stories.

In addition to asking Lauer about the rumored allegations, the network searched its human-resources and legal archives to see if there were any complaints or settlements involving Lauer, the network executive said. They found none, although Lauer has been the subject of tabloid rumors about infidelity for years.

People at the network also shed some light on one of the more lurid aspects of Variety's story: that Lauer had a special button at his desk that enabled him to close and lock his office door without getting up, thereby allowing him "to welcome female employees and initiate inappropriate contact while knowing nobody could walk in on him," as Variety put it.

The mechanism was a standard feature in many of the older offices at 30 Rockefeller Center, NBC's longtime corporate home, according to people familiar with the building's operations. The buttons were installed years ago by General Electric, which owned NBC for years and shared office space with the network.

The feature was a perk for top executives who wanted privacy for personal calls and meetings or as security in the event of a calamity — such as an active shooter within the building. Anyone inside such an office, however, could exit without using the button. It's not clear how many people at NBC News had offices equipped with the device.

In a memo to employees Friday, Lack called Lauer's behavior "appalling," and said the network would undertake a review "of what happened and what we can do to build a culture of greater transparency, openness and respect for each other." The review will be overseen by people from NBC's legal and human-resources departments.

Lack also said the news division would expand its sexual-harassment awareness training.

Lauer issued a statement Thursday that read in part, "There are no words to express my sorrow and regret for the pain I have caused others by words and actions. To the people I have hurt, I am truly sorry. As I am writing this I realize the depth of the damage and disappointment I have left behind at home and at NBC."