The Tweet clearly says they fired in him the first week and confronted him about the lying/scamming. It seems very clear that they figured it out right away and confronted him about it.

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oldgradstudent 9 days ago | parent [-]

But they haven't checked his employment eligibility or he wouldn't have started his first week.

	▲	FireBeyond 8 days ago \| parent [-]
		Legally, you have three days to complete an I-9 after starting a new position. Given that there's no oversight of the verification process, that can slide, too.