The first line of the Wikipedia entry on Martin Armstrong says:
Martin Arthur Armstrong (born November 1, 1949) is an American self-taught economic forecaster and convicted felon who spent 11 years in jail for cheating investors out of $700 million and hiding $15 million in assets from regulators. https://en.wikipedia.org/wiki/Martin_A._Armstrong
He was thrown in jail on contempt charges sometime in 2000 (I can't find the exact date). The contempt was for his refusal to turn over gold bars, gold coins and antiquities worth about $15 million. He claimed that he didn't have them. He sat in jail for 7 years until sometime in 2007 he was coerced to pleading guilty to fraud, and then he spent another 4 years in prison and was released on Sept 2, 2011.
What were the fraud charges? There were "24 related counts of conspiracy to commit securities fraud, commodities fraud, and wire fraud" and the Japanese investors lost nearly $1 billion. In his plea bargain, he plead guilty to one of these counts.
In 2017, some of the gold coins appeared. A thrift shop was going to auction them off, and Martin Armstrong popped up and said they were his. The US government now may have them (it isn't clear), or the bankruptcy receiver may have them.
Did Armstrong lie about not knowing where he hid the gold coins? It seems so, but why didn't he just dig them up when he got out of prison - did he forget where he buried them? Were they part of a different stash of gold coins, separate from the $15 million stash? That seems like a stretch. If he did truly forget where he buried them, does that help against the contempt charge, since he was unable to comply?
Armstrong claims he is innocent of the fraud charges. Maybe he is. A person is presumed innocent until proven guilty. He never faced a trial, because he pled guilty. But a guilty plea must be made willingly, and he didn't make it willingly. But if a defendant is going to challenge a guilty plea, he has to do it within a certain amount of time (6 months?). Did he challenge it within the time frame? Are their extenuating circumstances?
I see a Supreme Court petition that he filed that raises some of these issues:
At the outset, Armstrong was deprived of the ability to use his own untainted assets to secure counsel of choice. In the middle of this case, Armstrong was deprived of his liberty, confined to a prison cell for more than a decade on a charge that carries a five-year maximum. And now at the end of this case, Armstrong has been deprived of the untainted personal property the court-ordered receiver seized from him two decades ago. Needless to say, if a criminal defendant has a constitutional right to use untainted assets to secure counsel of choice, then he has no less of a constitutional right to the return of those assets that are not subject to forfeiture. https://www.supremecourt.gov/DocketPDF/19/19-392/116539/20190920142602151_2019-09-20%20Armstrong%20cert%20petition.pdf
Here is the reply brief: https://www.justice.gov/osg/media/1047066/dl?inline=
The Supreme Court denied his petition. https://www.scotusblog.com/case-files/cases/armstrong-v-securities-and-exchange-commission/
In conclusion, yes he is a convicted felon. But the way the case was prosecuted seems unfair, in particular the use of contempt of court in order to coerce a plea bargain. I wouldn't invest money with Martin Armstrong. But I do want to hear what he has to say.
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Update: This is Martin Armstrong in his own words explaining why he pled guilty:
The civil contempt was used to force me to plea for I was never entitled to a trial. The government said I could be held in prison indefinitely until I die and even denied me a lawyer. That was inside a tower in New York never being allowed to see grass again or feel rain. The compromise was that I would plea but refuse to ever say I stole anything. All I had to say to end the confrontation was about the bank stole the money – not me. https://www.armstrongeconomics.com/armstrong-in-the-media/armstrong-trial/supreme-court-status/