The second question most people ask with respect to Hendrik Schön is "When did he start faking data?"
(The first question is either "Why did he do it?" or "How could he possibly think he could get away with it?" Neither of these questions can be answered without a Vulcan mind meld.)
In our investigation committee, we did not seek to answer this question, only to pursue allegations that were brought to our attention, either directly or through Bell Labs. In fact, as the number of papers under suspicion grew from five to 25 or so, we realized we needed to close the door to new allegations, and we set an arbitrary cutoff date of June 20, 2002. We had plenty of material to work with for our report.
It turns out that a few days later we got another allegation that gave a strong hint that the faking began when Hendrik was in graduate school at the University of Konstanz, before anyone at Bell Labs knew anything about him.
To be honest, we were somewhat relieved that the new information came in after the cutoff, because investigating it would have involved us in a completely new class of materials and measurements, as well as new co-authors (obviously none from Bell Labs). We also did not have access to the digital data that was so useful for the other papers, and our authority to investigate this work would have been somewhat questionable, since we had been invited in by Bell Labs.
As we would later be told, Hendrik's thesis was rather unexceptional: lots of slow experimental work trying to accomplish a rather mundane task of introducing electrically active dopants into potential solar-cell materials. Reportedly, he was not having much success despite stead efforts, but at some point he suddenly reported dramatic success in doping the materials.
There were several different experiments on different materials with different dopants. Three figures from the papers are overlaid in this animated gif:
At least in the context of the other clear cases of copying, this looks pretty clear. Obviously not all the curves are the same, but some are, and the three figures are represented as coming from three different materials. However, the committee never examined this case in detail, so there may be important caveats.
The University of Konstanz decided in 2004 to rescind Hendrik's doctorate, deeming him "unworthy." This retroactive action struck me as rather odd. A court concluded in 2010 (amusing translation here; follow either link for a relatively recent picture) that the revocation was inappropriate, but in 2011 that decision was reversed.
In 2003, Jennifer Couzin reported in Science that "a committee at the University of Konstanz examining the work of disgraced physicist Jan Hendrik Schön found inconsistencies in several papers Schön published during his studies there, but no proof that he had deliberately manipulated data."
But I think we know he had already started down the path.