The source of that information is, mostly, from the part of the declaration of Spanair's chief of maintenance, Jesús Torralba A., made to the police on Aug 23rd where he says:
"I came to work at 6:45 that morning .... At the moment of the problem (the RAT heater issue) I wasn't told anything (nobody informed him about it). I was never involved in the resolution of the case, since the airplane was never out of service (AOG, Aircraft on ground, where the airplane is not fit to fly) ..."
"... The certifiers as well as the local supervisors in service can resolve this type of incidencies w/o informing the chief of maintenance, since they hold a licence for servicing this type of aircrafts. In the case that the airplane was AOG, it would've had to be reported to the chief of maintenance .... I was at the office of the company in Dique Sur when my local supervisor on service told me he had received a call from operations of a possible accident of an Spanair a/c. I looked outside the window in my office and I noticed the smoke mushroom. I went to the area and I reported back to my superiors that, indeed, the airplane was a Spanair ..."
The link below to the BMJ states that 70% of aviation accidents have human error at the root.
Basically all studies about aviation accidents cite human error as the main cause in the majority of cases. The ones I've read with the lowest number estimates over 60%. The ones with the highest: 80%.
It seems to be accepted in the industry that at least 66% of them are due to human error as the main factor. Roughly 25% due to mechanical/electrical malfunctions and roughly 10% due to weather and other issues as the primary cause.