Final answer:
The last step is to implement corrective actions based on root cause analysis, which involves a thorough understanding of the event timeline and differentiation of cause and effect.
Step-by-step explanation:
The last step of the four-step systems approach to conducting an incident investigation is to implement corrective actions to prevent future incidents. This step follows after identifying root causes and analyzing the incident. It is critical to undertake root cause analysis, which delves into the real cause of the problem rather than just addressing superficial symptoms. When conducting an investigation, one must gather information from relevant parties, consult expert sources, and maintain a clear understanding of the timeline of events - what happened first, what happened next, as well as differentiating cause from effect. This orderly approach ensures the analysis is thorough and correct, ultimately guiding the implementation of effective preventive measures.