1. Open Source Intelligence (OSINT) Tools: These are free tools that can help investigators gather information from publicly available sources such as social media, news articles, and government databases. Some popular OSINT tools include Maltego, SpiderFoot, and Shodan.

2. Law Enforcement Intelligence Databases: Law enforcement agencies have access to databases that contain information on criminal records, arrest warrants, and other relevant information. Some examples of these databases include the National Crime Information Center (NCIC) and the Integrated Automated Fingerprint Identification System (IAFIS).

3. Investigative Software: There are many software programs available that can help investigators manage and analyze large amounts of data. Some popular investigative software programs include Palantir, IBM i2 Analyst's Notebook, and CaseMap.

4. Professional Associations: Joining a professional association can provide investigators with access to training, networking opportunities, and resources. Some examples of professional associations for investigators include the International Association of Crime Analysts (IACA) and the Association of Certified Fraud Examiners (ACFE).

5. Online Training Courses: There are many online training courses available that can help investigators develop new skills and stay up-to-date on the latest investigative techniques. Some popular online training courses include those offered by the National White Collar Crime Center (NW3C) and the International Association of Computer Investigative Specialists (IACIS).