In an ideal world, salary would be a negotiated compensation for the value you provide the employer. It's hard to make arguments based on peers, because individual skill levels and performance can vary. Of course, if you're making 60% less than people who you're obviously outperforming, that's an issue. But in many employers, there may be legitimate variances between individuals with the same title, due to differences in performance or skills.
And at the end of the day, you should want to be paid what you are worth, not what your coworker is worth. So - before making any argument for a raise, be prepared to back it up based on the current and future value you are providing. To play devil's advocate, imagine if you based your argument only on the assumption that you and your coworker are worth the same amount - what's to stop your employer from just giving them a pay cut to equalize the salaries? After all, that would result in equal pay.
And, as a final thought, consider: acts of sabotage are sometimes done with specific motivations in mind. People who are willing to break policy or distribute private information on their way out the door may not be the most trustworthy sources.