The report from News of the United States (NOTUS) says a woman, whose name is not mentioned in the report, came forward and filed the complaint after she had a more secure position in Congress and wasn't concerned about losing her job.
The woman claimed Costa repeatedly asked her to dance and made advances toward her during an event in February of 2020, while she worked with a different lawmaker.
The woman also alleges she witnessed an incident involving Costa and a female intern in December of 2021.
The Office of Congressional Conduct (OCC) and the House Ethics Committee both moved to dismiss the case, citing not enough evidence to proceed.
In a statement on Monday, Costa's office said he cooperated with the investigation and that the actions of the OCC and the Ethics Committee speak for themselves.