Fisher delivered the news to Williams on Wednesday that the franchise would be cutting ties for at least the 2012 season, under the assistant's indefinite suspension from the NFL for the bounty payments that he handed out with the Saints.
Fisher betrayed no emotion at a news conference at which he said the punishment was "warranted."
"The severity of the suspension does not surprise us," Fisher said. "We, as best you can, have been preparing for that."
Fisher said Williams will be eligible for reinstatement after the 2012 season, but gave no guarantee that he'd want Williams back saying, "You know, we'll cross that bridge when we come to it." He did, however, lavish praise on a man who consistently has produced top 10 defenses.
"I don't mean to be insensitive to this, but we have to move on," Fisher said. "Our job's to win games and Gregg's got to learn from his mistakes, and he's paying dearly for them.
"He's going to do his best to do whatever it takes to get reinstated."
Williams did not argue with the terms of the suspension and said, "I accept full responsibility for my actions." He said pledged to cooperate with the league in its ongoing investigation, and said he would serve as an advocate for player safety and sportsmanship.
Williams added that he'll do anything he can to earn back the respect he has lost, and wants to return to coaching.
Before meeting with media, Fisher watched commissioner Roger Goodell being interviewed on TV, and began his news conference by saying: "Not an easy day for him. Not a good day for the National Football League."
Fisher seemed to offer as much support as he could when asked why he thought one of his close friends would act this way.
"There's a great deal of information out there that we will never know, so I can't really comment on the specifics of that and place blame on anybody," Fisher said. "Never, at any time, as far as I've been with him, has he disrespected this game from the standpoint of you try to hurt somebody on purpose.
"He has a passion for this game and a passion for playing hard-nosed, aggressive defense. I think there's a lot out there that will probably be locked up in a drawer some place."
Fisher said he'd be part of a committee of coaches replacing Williams and likely wouldn't hire another assistant. Fisher is a former defensive coordinator, pointing out that he's the originator of the Rams playbook and he has two other people with experience at that position on his staff, assistant head coach Dave McGinnis and defensive backs coach Chuck Cecil.
"So I have a pretty good feel for the defense," Fisher said. "At this point I'm not at liberty to say who's going to make the calls and the decisions, but it'll get done and it'll get done effectively."
Fisher was adamant that the franchise, and Williams, had been unaware of the NFL investigation.
"I know Gregg and I know him well," Fisher said. "Gregg would not have put this organization in this position, accepted this job, only to be suspended, and put us behind the 8-ball if you will."
The suspension was a jolt to Fisher's rebuilding efforts in St. Louis, which has totaled just 10 victories the last three seasons. Williams was a head coach for three years - in Buffalo - and a defensive coordinator for 13, regularly producing defensive numbers among the NFL's best, and was Titans defensive coordinator under Fisher when Tennessee lost to the Rams in the 2000 Super Bowl.
Williams arrived promising a culture change for a franchise that ranked near the bottom of the NFL against the run and often folded late. He remained on the job after the bounty scandal surfaced on March 2.
Said Fisher: "I would say he's somewhat surprised, shocked, disappointed, but also remorseful."