An Ohio-based rapper said that he received an email from Gavin Long just an hour before he went on a rampage in Baton Rouge, Louisiana killing three police officers.
Yarima Karama said in a video posted online that the email included images of a three-page, handwritten letter.
The subject line of the email was "manifesto."
The manifesto's opening is largely copied from Christopher Dorner, the former police officer who went on a shooting spree in Southern California in 2013.
Much of the document is concerned with police corruption and what the writer sees as the system's failure to prosecute bad cops.