No he didn't. You're thinking of Enron. Tyco is a thriving business with 260,000 employees, whose stock did no worse during the 2001-2003 market dump than did Amazon, Yahoo or Apple. What he did was awful indeed, but is hardly worth 25 years or brutal sodomy, as many here have suggested.
I like all these convictions as they send a message to CEO's that there are some limits on their predations on their companies. It also tells their subordinates that there can be consequences for emulating their bosses' worst habits.
I guess that the real problem is that a big public company really has too many shareholders for a unified voice over a CEO. It's just very difficult to get enough shareholders together to crack down on misbehaving executives. So an unethical executive has little to fear.