Hagmann Investigative Services, Inc. is a professional and licensed Private Investigative Agency with its main office located in Erie, Pennsylvania.  Douglas J. Hagmann is the licensed principal of the corporation and personally handles or directly superintends each investigation assigned to the agency.

Douglas J. Hagmann served a three year apprenticeship as an investigator from 1984-1987, completed numerous internal and external investigative training courses and became licensed as a private investigator in 1987.  During this apprenticeship, Douglas Hagmann was the primary investigator in 900 separate investigative assignments that included insurance fraud, missing persons, domestic concerns, and unsolved homicides.  Between 1987 and 2007, Mr. Hagmann was the primary investigator in over four thousand separate investigations, including over 40,000 hours of covert surveillance operations throughout the eastern United States. 

Between 1996 and 1998, Mr. Hagmann was utilized by the United States Department of Justice as an informational and operational asset in several undercover interstate criminal investigations. During that same period, he worked closely with the Pennsylvania State Police as an operational asset in related cases.

In May 2002, Doug Hagmann received certification on the Physical Significance of Bloodstain Evidence at the Laboratory of Forensic Science in Corning, New York. Mr. Hagmann possesses many law enforcement related training certifications, including to Surveillance strategies, Fundamentals of Investigations, Fraud Identification Strategies, and Computer Investigation Strategies. 

In 2003, Douglas Hagmann authored Tactical Surveillance - an investigator's guide to conducting surveillance [ISBN 978-0-9796479-0-1]. The book has sold over 5,000 copies and has been well received by investigators in both the private and public sector.

Following the attacks of September 11, 2001, Hagmann began using his investigative skills and training to fight terrorism and increase public awareness by establishing the Northeast Intelligence Network.