Does the complaint, on the face of it, meet the definition of harassment? In other words, if proven, would the allegation or situation amount to harassment according to the definition? If the answer is yes, law uses the Latin term “prima facie” to describe the case.
Of course, the case is not proven at this point as no evidence other than the complainant’s statements have been obtained.
If there is no prima facie case of harassment, approaches other than investigation should be considered.