Speaking to reporters in Riga, Latvia, before a meeting with European Union justice ministers, Lynch did not hint as to whether charges against Blatter were a possibility.
“It's an open case and so we will now be speaking through the courts," Lynch said.
Still, Lynch expressed optimism that Blatter's resignation would signal change at FIFA. She said she hopes FIFA "will be able to move forward in a way that is supportive of its goals, which are the promotion and regulation of a truly wonderful sport."
In regard to allegations FIFA officials may have accepted bribes in matters related to the awarding of the 2018 and 2022 World Cups, Lynch said that was not the primary focus of the U.S. investigation. She said the ongoing Swiss probe is investigating matters related to possible infractions tied to the World Cup bids.
Last week, the U.S. attorney general's office unveiled an indictment of 14 high-ranking soccer officials and businessmen, citing a pattern of bribery that it said spanned decades and totaled more than $150 million.
Times staff writer David Wharton and the Associated Press contributed to this report.