This series of Invoice Records was maintained and compiled in whole or in part while the Baltimore City Police Department was a state agency. For a general introduction to the history of the Baltimore City Police Department, see https://guide.msa.maryland.gov/pages/series.aspx?ID=sh248. Also, for additional information, see the following privately maintained website: http://wayback.archive-it.org/2504/*/http://www.baltimorecitypolicehistory.com/.