I don't think it would be necessary in the case of federal employees. The situation becomes more problematic—and I don't know how much you have taken this into account—when national safety issues involve all stakeholders. I think that 17 departments were talked about. In reality, there is still some pretty close collaboration with provincial and municipal police forces.
If your committee was considering a major case, you would no doubt see that authorities outside the federal government were involved. As I am not a lawyer, I cannot tell you whether that requires subpoenas or other measures. I don't really have an opinion on that. However, I can see that testimony from outside the federal government could be desirable.