An apex deposition of the head of a governmental department is allowed only with the agency head is shown to have direct personal factual (as opposed to legal) knowledge of information pertinent to material issues in litigation and the agency head’s information is not available through another source. Here, an apex deposition of the former district attorney was not allowed on issues relating to the prosecutor’s union since they were not closely tied to plaintiff’s employment retaliation claims. But the deposition was allowed as to the district attorney’s having been told by other prosecutors to change his testimony about the ethical shortcomings of his successor in office since the successor was the one who fired plaintiff, and his credibility was a key issue in the case. And the effort to change a witness’ testimony is relevant as evidence of defendant’s consciousness of guilt.