Prosecutors in the US state of Georgia are investigating attempts by former President Donald Trump to overturn results from last November’s election.
Mr Trump was recorded telling the state’s top election official to “find” more than 11,000 votes, enough to give him victory there.
The official is heard replying that Georgia’s results are correct.
Joe Biden’s win in Georgia and other swing states secured him the presidency.
Fulton County District Attorney Fani Willis sent a letter asking state officials to preserve documents including those relating to the phone call and saying that a criminal investigation was being carried out.
“I just want to find 11,780 votes,” Mr Trump told Georgia’s Republican Secretary of State Brad Raffensperger in a recording of the call released by the Washington Post last month.
In the months after the election, Mr Trump made unsubstantiated allegations of widespread electoral fraud and claimed that votes were stolen from him.