The inquiry is focused on $10 million that the charity received last year, then gave to political committees that helped Gov. Ron DeSantis defeat a ballot measure.
The aquatic park, a South Florida landmark for 70 years and also the subject of complaints over animal rights, drew visitors on Sunday before closing for good.
President Trump has not revealed any concrete plans for a future library, but his son and others have been scouting possible sites in South Florida for months.
A jury found Donna Adelson guilty of murder in the 2014 death of her former son-in-law, Dan Markel, a Florida law professor. She is the fifth person to be convicted in the high-profile case.