Police said on Thursday they closed a yearlong preliminary investigation into allegations that Lee Boo-jin, eldest daughter of Samsung Chairman Lee Kun-hee and chief executive of Hotel Shilla, abused a controlled substance, as they found no evidence that she did.

“No evidence to prove Lee’s illegal injection (of propofol) has been found, so we closed the internal investigation,” the special detective division of the Seoul Metropolitan Police Agency said.

Police said that propofol was used in a procedure that Lee underwent at a plastic surgery clinic in Gangnam in 2016, but experts said the injected amount was not enough to constitute abuse.

In an interview with an online news outlet Newstapa last year, a nurse’s aide at the clinic claimed that Lee regularly used the anesthetic from January to October 2016.

Since March last year, police searched the clinic several times, secured medical records including their drug control book, and questioned Lee as well as the clinic’s staff.

Police have referred the head of the plastic surgery clinic to the prosecution, with a recommendation to indict on charges of medical law violation, and two nurse’s aides with a recommendation not to indict.

By Kim So-hyun (sophie@heraldcorp.com)