[ideophobia]

According to the DOJ press release from January, "under the terms of Lieber’s three-year Thousand Talents contract, WUT paid Lieber $50,000 USD per month, living expenses of up to 1,000,000 Chinese Yuan (approximately $158,000 USD at the time) and awarded him more than $1.5 million to establish a research lab at WUT." [1]

I suspect they had evidence to indicate he was paid, but couldn't produce specific financial records to prove it without a doubt. In cases like this, the FBI typically goes for the jugular by pursuing espionage charges. This can be difficult because it often requires concrete evidence of financial gain from the foreign entity explicitly for the information provided or actions taken. The mere appearance of financial gain is not enough, they'd want to see the literal check stubs and account statements.

[1] https://www.justice.gov/opa/pr/harvard-university-professor-...