The US justice department said on Wednesday it had obtained a warrant to search the phone of Donald Trump’s election attorney, John Eastman, who spoke at a rally before the January 6 assault on the US Capitol.

Federal agents seized Eastman’s phone in June based on a warrant authorizing them to take the device. They needed a second warrant to search the phone’s contents.

In a filing with US district court in New Mexico, the assistant US attorney Thomas Windom said the US district court for the District of Columbia issued a search warrant on 12 July authorizing review of the phone’s contents and manual screen capture.

He said federal agents in northern Virginia had the phone and screenshots of some of its contents.

Eastman has been under intense scrutiny in the investigations into the attack on the Capitol by Trump supporters after the former president falsely claimed that he had won the 2020 election. Eastman spoke at the rally where Trump gave a fiery speech alleging election fraud and urging supporters to march on the Capitol.

Eastman also wrote a memo outlining how, in his view, Mike Pence could thwart formal congressional certification of Trump’s re-election loss. The then vice-president declined to follow Eastman’s advice.

Wednesday’s filing was made in New Mexico because Eastman had previously filed a suit there asking a judge to order the justice department to return the phone, destroy records and block investigators from accessing the phone.

The judge denied that request but ordered the government to update the court by Wednesday on the location of the phone and status of a second search warrant.

A representative for Eastman was not immediately available for comment.