The trial of Vital Kamerhe -- who remains the president's chief of staff -- has gained widespread attention in the country where high-profile figures are rarely brought to court.
Kamerhe has insisted he was not in office when the contract at the centre of the allegations were signed in April 2018.
On Thursday, during proceedings that ran to almost 13 hours and were broadcast live from the prison he has been held in since April, he said he "could not take responsibility without the knowledge of the president."
Lebanese businessman Jammal Samih got a contract to build 1,500 new prefab homes "with the express instruction of the head of state," he said.
Kamerhe and Samih both deny allegations of wrongdoing.
A government advisor later called by the prosecution slammed Kamerhe's comments as an insult to the president.
Trial proceedings had resumed Wednesday, a week after the sudden death of the presiding judge Raphael Yanyi, who died following a heart attack, according to police.
The results of an autopsy are awaited.
Kamerhe was a pillar of the regime of former president Joseph Kabila and initially stood in the 2018 presidential poll but bowed out to team up with Tshisekedi.
His supporters charge the case is politically motivated -- they portray it as a likely attempt to prevent him from running in the next presidential election in three years' time.
The trial comes as Tshisekedi -- who took office in January 2019 in the first ever peaceful transfer of power in the country -- runs a campaign to root out entrenched corruption.
The biggest country in sub-Saharan Africa, DR Congo has an abundance of natural resources, but two-thirds of its 80 million people live in poverty.
The country struggles with a long history of conflict, poor governance and graft.