The shooter, identified as 29-year-old black male Gavin Long of Kansas City, Missouri, is listed on the Servicemembers Civil Relief Act (SCRA) website as having joined the Marines in August 2005 and ended active duty in August 2010.
Military records released Sunday night show he made the rank of Sergeant and was a Data Network Specialist. He deployed to Iraq once, from June 2008 to January 2009, and also served at a Marine Corps base in Okinawa, Japan, the records say.
Other public records appear to show Long was married in 2009 but petitioned for divorce just two years later.
Federal authorities are currently looking at ties Long may have had to an anti-government group that Long apparently showed support for online, according to a source familiar with the probe. The group, called the Moorish Science Temple of America, was founded in the early 1900s and does not recognize U.S. government authority over the descendants of slaves, according to court documents in an unrelated lawsuit.
Roger Brewington Bey, a spokesperson for the Moorish Science Temple of America, said that Long never joined any of the organization's temples. "Nothing in our teachings espouses those types of criminal activities," Bey said. "Our founder made the statement in 1928 that the teachings were to make our people better citizens, not make them outlaws."
Long was carrying his cell phone during his assault and it has been recovered by law enforcement, the source said. The source said Long apparently rented a car in his hometown of Kansas City, Missouri, and drove the more than 700 miles to Baton Rouge.
Long killed three police officers and wounded three others before being gunned down himself, officials said. Authorities initially suspected other shooters could be on the loose, but have since determined Long appears to have been a lone gunman. Records show today was Long's birthday.
ABC News' Justin Fishel and Gina Sunseri contributed to this report.