Bernard Madoff, who cultivated a worldwide mystique as he churned out amazingly steady returns for his investors year after year, finally admitted it was all a lie, saying he had felt compelled to deliver at any cost.

If his thousands of customers were expecting deep insight into why he did it, they were disappointed.

The silver-haired money manager, wearing his signature gray suit and showing little emotion, offered an apology and an explanation of sorts in a 10-minute courtroom monologue. While saying he was actually grateful for the chance to speak, he did not dwell on the motive behind his crime spree.

Madoff said he wanted to keep investors seeking good returns happy and that, once he started, he could not stop.

While I never promised a specific rate of return to any client, I felt compelled to satisfy my clients' expectations, at any cost, he said on Thursday, standing and reading his statement to the court in a steady voice.

Madoff's statement, delivered as a judge accepted his guilty plea on 11 criminal counts and sent him to jail, was at odds in places with prosecutors' version of events.

His remarks also caused eyes to roll among investors, who said they did not believe his apologies were sincere.

It's just a standard statement from a guilty person, said Judith Welling, 70, of Manhattan, who invested more than $1 million with the one-time Nasdaq chairman.

Sitting with her husband, she sighed at times and shook her head in frustration as they watched Madoff on a video feed in another part of the Manhattan federal courthouse.

As Madoff told it, the scheme started when financial markets were struggling amid a U.S. recession and new deposits were flowing in from institutional clients that he felt obligated to accept.

He turned to crime to keep these investors content. He concocted a fictitious split strike conversion strategy that he marketed to investors, then provided fake financial statements so they would think they had the investment results I believed they expected.

Madoff said he hoped to end the scheme in short order, but it spun out of control.

His account conflicted with the one provided by prosecutors in court papers. Madoff said, for example, that to the best of my recollection his fraud started in the early 1990s.

Prosecutors believe it dates back the 1980s or even earlier. Acting U.S. Attorney Lev Dassin said in a statement after the proceeding: We do not agree with all the assertions made by Mr. Madoff today, but his admissions were nonetheless more than enough to establish guilt.

Investors also complained they thought Madoff had not come completely clean. Ronnie Sue Ambrosino, 56, urged the judge to force him to provide more details.

I believe that you have the opportunity to find out information about where the money is and who else was involved, she said at the hearing.

Another investor demanded that Madoff, who mostly looked straight ahead with hands folded during the proceeding, at least acknowledge the people he cheated. The investor challenged Madoff to turn around and look at the many victims who filled the courtroom.

His investors and the public had long waited for him to break his silence. Now he is not expected to speak again publicly until his June 16 sentencing date.

Mr. Madoff, I will see you upon sentencing, Judge Denny Chin said as he ordered the swindler to jail.

(Editing by Andre Grenon)