In what circumstances will a defendant be charged with perjury in falsely testifying that he does not remember certain criminal acts?

In People v. Doody the defendant was charged with perjury in falsely testifying that he did not remember certain criminal acts. The evidence established that he had sworn to the commission of these acts in conspiracy with a number of confederates in the course of a number of previous trials, as well as before the grand jury. Two or three days before the trial at which the perjury was committed the district attorney read over to him the evidence he had previously given and Doody admitted such evidence was correct. At the trial he swore he did not remember any of the facts to which he had previously sworn.