By cops I meant FBI/... And the way this is done is you notify the cops first and then coordinate with them if needed. It's not like Twitter learned about this 5 minutes before.
The FBI obviously doesn't enforce internal company policies. However, if the company has evidence that the employee is engaging in serious violations of the Computer Fraud and Abuse Act (CFAA) of 1986, or engaging in espionage for a foreign power, then the FBI might send agents to investigate.