The motor home was parked in an alley behind a vacant business in the 500 block of West 17th Street near Magnolia Avenue. Authorities would not say why they're investigating this case as a homicide. The coroner removed the body late Tuesday morning.
Long Beach police officers smelled smoke and located the vehicle on fire just after midnight.
"Officers alerted Long Beach Fire Department and then using extinguishers they had in their vehicles, extinguished the flames. When fire department arrived and checked the vehicle, they found that there was a deceased adult inside," said Marlene Arrona with Long Beach police.
Workers in the area say the man living in the RV often walked his dog. They described him as a very friendly man.
Police say they did find a dog in the area. The coroner will determine how the man died, and how the fire started is under investigation.
At this point, police are investigating the death as a murder and say the circumstances are suspicious.
"It is unusual that a vehicle be in flames and to find a deceased inside. So with that in mind, detectives were called out - both the arson investigators as well as homicide investigators - to piece together what may have happened here," said Arrona.
The identity of the victim was not immediately released.