Police in Germany reportedly discovered documents indicating that Andreas Lubitz—the co-pilot of the Germanwings plane believed to have been intentionally crashed, killing 150 people—may have been hiding a medical condition from his employers. Investigators also claim to have found a torn up doctor's note excusing him from work.

The documents were obtained by police from two locations: Lubitz's apartment in Dusseldorf and his parents' home in Montabaur.

German investigators have not made public what medical condition Lubitz may have been suffering, but told the New York Times that "documents were secured containing medical information that indicates an illness and corresponding treatment by doctors." Investigators said they did not find a suicide note or any "indication of any political or religious motivation."

The shredded sick note, however, is not necessarily conclusive: As the Associated Press reports, "sick notes from doctors excusing employees from work are common in Germany and issued even for minor illnesses." More from the AP:

The U.S. Federal Aviation Administration had issued Lubitz a third-class medical certificate. In order to obtain such a certificate, a pilot must be cleared of psychological problems including psychosis, bipolar disorder and personality disorder "that is severe enough to have repeatedly manifested itself by overt acts."

The certificate also means that he wasn't found to be suffering from another mental health condition that "makes the person unable to safely perform the duties or exercise the privileges" of a pilot's license.

Police have not responded to stories in German media that have described Lubitz as having suffered from a history of mental illness and depression, citing their ongoing investigation.