Hello and welcome,
Although the tax preparer may be held liable for misrepresentations made on a tax return, unless the preparer is defrauding the client in some manner, criminal charges are not normally brought against the preparer of the returns.
Here is a link that provides examples of criminal convictions of tax preparers:
However, since it does appear you knew that some returns provided false information, it would be best first to retain a local attorney to represent you before reporting the issues to the authorities. You would normally gain whistle blower status, so your job should be protected from retaliation if you report the employer, but it is best to have a local attorney advising you prior to reporting the employer so you do not incriminate yourself in some manner and avoid the possibility of criminal charges being filed, although it is normally unlikely that they would be unless you are benefiting in some manner from the deceit.
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