If you authorized a credit report to be run in order to check your creditworthiness as a tenant, it should not matter that it was not run immediately. You were still a tenant when it was run. However, you need to provide a lot more details about this "harassment" and "threats" because those might be the basis for a separate claim. You can contact my office to discuss this further.
From the facts you have given, I can not say whether they had a permissible purpose. Was any money owed under your lease at the time they ran the credit report? Had the lease expired? If they had any claim for additional sums owed, then they probably had a legitimate business purpose for running your credit. If you had satisfied all obligations under the lease, the prior credit arrangement would not give them permission to run your credit in the future.
Under the Fair Credit Reporting Act, one must have a permissible purpose to both obtain and use a consumer report on a consumer. If a consumer report is obtained without a permissible purpose under the FCRA or is used for an impermissible purpose, then the law is violated. Pre-litigation research into the assets of a potential defendant/opposing party to a lawsuit is generally prohibitted, though some courts have found permissible purposes in limited circumstances. If harassment was truly the purpose for either obtaining or using the report, then it certainly sounds like a violation of the act. The issue then becomes one of proof--that is proving that the real prupose was harassment. I have included a link below to the FTC website containing the list of permissible purposes under the FCRA. Note, there is a 2-year limitations period under the FCRA, which limits the time for an individual to file a claim to enforce remedies under the act.