Walsh said he was told to tape opposing coach's signals shortly after Bill Belichick was named head coach in 2000.
"The most important thing is winning and don't get caught," he said. "I kept my season tickets in 2003 and 2004 (and) I went to every home game I could. It extended beyond me. Through binoculars, I would see the third video assistant doing the same thing."
Walsh said he is not disgruntled about being fired in 2003 and finds Belichick's claim that he did not know him difficult.
A New England employee was caught videotaping New York Jets coaches during the 2007 season opener. NFL Commissioner Roger Goodell fined Belichick $500,000, fined the team $250,000 and required the Patriots to forfeit their first-round pick in the 2008 NFL Draft.
Walsh said he no longer owns season tickets.