Three Components of Circumstantial Evidence
1) raising an inference of retaliation - Because you don't have direct evidence you have to show the implications of your evidence by building a thorough case against your employer and its arguments/positions;
2) if your employer fails to produce evidence of a legitimate, non-retaliatory reason for the challenged action (firing, demotions, suspension, transfer to a hard to reach location, being stripped of assignments, harassment, retaliation, etc.) - Are your employer's reasons for its actions against you plausible/believable? You have to focus on exposing their lies and destroying their cover story; or
3) if the reason advanced by the employer is a pretext to hide the retaliatory motive - You can show pretext by demonstrating that your employer treated you differently than similarly situated employees (similar jobs/titles, location/job site, job levels/classification, etc.).
Also consider that an initial inference of retaliation arises where there is proof that the protected activity and the adverse action were related. Typically, the link is demonstrated by evidence that:
-- the adverse action occurred shortly after the protected activity; and
-- the person who undertook the adverse action was aware of the complainant's protected activity (opposing discrimination, participating in an investigation, etc.) before taking the action.
So, if you file a complaint against your employer, internally or externally, alleging discriminatory practices, retaliation, etc. and you suddenly become targeted with adverse actions like increased surveillance and heightened scrutiny, unjustified negative performance evaluations, denial of a promotion, etc., you should link the timing of filing your complaint with the timing of a quick response by your employer that included adverse actions. Point out that those engaged in executing the performance action knew of your complaint/oppostion to discriminatory practices.
Even if your employer waits to execute adverse actions, you can still prove retaliation, etc. through other circumstantial evidence.