In an interview published on Sunday in the Bild am Sonntag newspaper, Wulff said, "Of course everyone should be considered innocent until proven guilty. But separate of personal guilt, there is also political responsibility. The mayor will have to consider all these things very carefully."
Sauerland has refused to consider resigning so far, saying he will wait for the results of an investigation into the errors and incompetence that led to the deadly crush at the July 24 Love Parade.
But Wulff also warned against blaming only Sauerland for the tragedy in the North Rhine-Westphalia city of Duisburg. "All we know for sure is that no single person is responsible," he said.
"We all hold responsibility for the people of Duisburg," the president said. "A catastrophe has nothing to do with the question of where it happened, but how."
He said he could understand people's need to identify those responsible, and said, "Those who made mistakes have to be called to account."
Wulff intends to visit Duisburg again in mid-September, and he praised the speech delivered by North Rhine-Westphalia state premier Hannelore Kraft at Saturday's memorial service. "Even a politician has to show her emotions in such situations."