BERLIN (AP) — Former Volkswagen CEO Martin Winterkorn denied early knowledge of the company's cheating on diesel emissions as he testified Thursday to a German parliamentary inquiry — his first major public appearance since he resigned in 2015.

The 69-year-old resigned in September 2015, several days after news of Volkswagen's use of software to cheat on emissions emerged in the U.S., saying that he was not aware of any wrongdoing on his part.

"As CEO I took political responsibility," he told lawmakers Thursday. "Believe me, this step was the most difficult of my life."

Winterkorn, flanked by two lawyers, told the panel in an opening statement that "it is not the case" he knew earlier than previously thought of the scandal. He said he's still seeking "satisfactory answers" as to what happened.

Winterkorn said he wouldn't comment on details that are a matter for a criminal investigation by prosecutors in Braunschweig, Germany, and declined to answer several questions on exactly when he knew what.

The former CEO acknowledged that "love of detail" was his "trademark."

"It is not comprehensible why I was not informed early and clearly about the measurement problems," he said.

He added: "Of course I ask myself if I missed signals or misread them." He wouldn't elaborate on what those signals were, citing the ongoing investigation.

Winterkorn told lawmakers that he appreciates "open talk."

"I never had the impression that people shied away from talking openly to me," he said.

Volkswagen installed software on diesel engines that activated pollution controls during tests and switched them off in real-world driving. The software allowed the cars to spew harmful nitrogen oxide at up to 40 times the legal limit.

Winterkorn reiterated his "deep dismay" that Volkswagen disappointed millions of customers and underlined his commitment to clearing up the events at Volkswagen.

"What happened makes people angry — me too," he said.

But "I am a realist," he added. "I have to accept that my name is closely linked to the so-called diesel affair."

The German parliamentary inquiry was set up last July. It is tasked with looking into whether the German government knew about vehicles' emissions on the road diverging from their emissions in testing, and whether there were indications of the cause.