Court documents show a $1,000 donation was made in Dan Webb's name to Foxx's campaign in 2016.
Webb's law firm hosted a fundraiser for Foxx, but he says he does not recall making the donation.
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Jussie Smollett case: Timeline of key moments in alleged attack on 'Empire' actor
Foxx said she just learned about the donation last week and continues to cooperate with the investigation.
Webb is now investigating Foxx's decision to dismiss felony charges against Smollett, who's accused of staging an attack on himself.
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Smollett was charged with staging the attack in Chicago's Streeterville neighborhood in January. Police and prosecutors said Smollett orchestrated the attack with the help of two brothers. One brother was an extra on "Empire" and the other was Smollett's personal trainer.
All charges against Smollett were dropped in late February in exchange for community service and forfeiture of his $10,000 bond payment.
Previous coverage:
Jussie Smollett case: PR firm says 'every iota' of 'Empire' actor's claim true; police differ
Dan Webb appointed special prosecutor in 'Empire' actor's case
Jussie Smollett case: Hearing held on Chicago's lawsuit against 'Empire' actor
'Empire' filming in Chicago near Jussie Smollett alleged attack site
Jussie Smollett: Judge dismisses motions by 'Empire' actor's attorneys
Jussie Smollett: Attorneys decline special prosecutor role in actor's case, report says
'Empire' actor's attorneys argue against special prosecutor, want judge replaced
Jussie Smollett's attorneys argue for Chicago lawsuit to be moved to federal court
Chicago police release investigative files, video of alleged staged attack on 'Empire' actor
Judge orders special prosecutor to review Jussie Smollett case