Final answer:
The exact number of people killed justifiably by police in a three-year period cannot be determined based on the information provided.
Step-by-step explanation:
Based on the information provided, it is not possible to determine the exact number of people killed justifiably by police in a three-year period.
The statistics given refer to police deaths, not civilian deaths. In addition, the information only provides averages for specific periods of time, 2000-2009 and 2013-2014, and does not indicate the killings within those time frames.