Generally speaking anyone actively under indictment, on probation, parole or in a diversionary program is ineligible to obtain a TWIC card. There are, however, limited exceptions to the rule.
For example, if an applicant has a suspended criminal sentence then he/she is still eligible. Other less clear circumstances exist wherein an applicant may still opt to try and obtain his TWIC even if he/she does not fall under a clear exception. These circumstances include but are not limited to; a cooperating witness, an applicant with an indefinitely continued sentence date, or an applicant with the support of his pretrial, probation, or parole officer. To find out whether you may fall under one of the exception(s) takes a keen legal eye. Best of all, since no TWIC application is denied with prejudice (meaning you can always reapply after a denial) being aggressive in making your application instead of waiting may make the most sense.