In view of the considerable length of the police chief’s tenure as head of the department, the chief should be held accountable for the widespread corruption in the department.
Conclusion (should = opinion)
The chief should be held accountable for the widespread corruption in the department.
Evidence
The chief's tenure has been considerably long (and the lack of incriminating evidence doesn't exculpate the chief).
Evaluate
The first claim is the premise, because the author is saying, .
We can predict a Missing Link answer here like,
If you've been head of a then you department for a long time should be and → held that department has responsible widespread corruption
The final sentence seems like padding. It's saying, .
Goal
Look for an answer that provides a principle set up in this form:
if XYZ, then should be held responsible
The trigger needs to be applicable to the chief, so it should mention "long tenure / lack of incriminating evidence" or both.