According to his website he wasn’t really guilty, he just plead guilty to protect his family:
“In 1989, the government charged Milken with securities/reporting violations in a case that continues to engender controversy. He admitted conduct that resulted - during a brief period in his 20 years on Wall Street - in five violations. Although such conduct had never before (nor has since) been prosecuted criminally - a fact rarely mentioned in press reports - he resolved the case without a trial to prevent further impact on his family. After paying a $200 million fine and serving a one-year-and-10-month sentence, he resumed his philanthropic work.”
He plea bargained so that he only had to pay $200 million and spend 2 years in the pen. All done to protect his family. :)
BTW, he was, and probably still is, a big fundraiser/contributor for the Democrats. It’s funny that Republicans and Wall Street are linked together and branded as evil. When you look at all the people that helped make the 80s the “decade of greed,” they are all Democrats. Michael Milken, Ivan Boesky, etc.