Combining answers from your other question here -- you'll need to speak to an attorney. If you're an employee of the agency, you may be covered by federal whistleblower (or state, if it is a state agency) protections. Your liability to a defamation claim from the private company will depend on the facts, and is not something we could really answer on Avvo. Similarly, whether the fifth amendment will be relevant (e.g., if you are in a situation where you might incriminate yourself or implicate that right) will also be fact dependent. A disclaimer is honestly not going to do you very much, and in fact may hurt you in a potential private defamation case, as an indication that you do not believe the material to be true.
Like I said before, you should speak to an attorney familiar with whistleblower claims.
The author is a Maryland attorney; however no answer given on Avvo is intended as legal advice or intended to create an attorney-client relationship. Dan's expertise lies in the electronic entertainment (video game) industry, as well as complex internet law issues, electronic free speech, entertainment law, copyright and trademark law, and computer fraud. He primarily represents game developers and founders of emergent internet technologies.
Please note that I am not licensed in your state so my comments are general and have no specificity to state law in Illinois. Whistleblowers are always subject to retaliation and that is why many states and the federal government have enacted legislation giving them certain rights. Having said that, as an employment lawyer, it has been my experience that employees who blow the whistle get punished by being demoted, terminated, being frozen out by their co-workers and bosses, getting their overtime taken away, being assigned too much or not enough work, and even having their family members punished. In order to avoid this scenario the only thing that I can think of is that you can make an anonymous report or ally yourself with some member of the legislature or the government to get help under their auspices. Another idea is to band together with a group of employees who want to blow the whistle. However, again in my experience as an employment lawyer, people on the payroll will support the one signing their paycheck by lying under oath any day of the week. My clients are constantly shocked by this, please don't be. I am sorry that you find yourself in this difficult situation and that it is likely that you must choose between your livelihood and your conscience. Good luck.