"to take the fifth"
to remain silent regarding a particular subject or circumstance in order to not incriminate yourself
answer, bridle, button, check, clam, close-lipped, curb, defer, discrete, discretion, evidence, grounds, hold, hush-hush, incriminate, inhibit, keep, law, oath, refrain, refuse, restrain, reticent, silent, suppress, testify, tight-lipped, uncommunicative, unforthcoming, zip
The criminal being questioned by the police detective is literally taking the fifth
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