"I did"? Did what?

Does "I did" mean "what I did (in the Stanford prison experiment)"? So the author refers to "what I did in the experiment is an evil of inaction"?

Context:

I wish I could say that writing this book was a labor of love; it was not that for a
single moment of the two years it took to complete. First of all, it was emotionally
painful to review all of the videotapes from the Stanford Prison Experiment (SPE)
and to read over and over the typescripts prepared from them. Time had dimmed
my memory of the extent of creative evil in which many of the guards engaged,
the extent of the suffering of many of the prisoners, and the extent of my pas-
sivity in allowing the abuses to continue for as long as I did - an evil of inaction.
I had also forgotten that the first part of this book was actually begun thirty