David Lemus-Orellana, 22, was arrested on Wednesday, according to the Los Angeles County Sheriff's Department.
The victim was identified as 64-year-old Florinda Velasquez-Hernandez, authorities said.
Authorities said a motive is unknown, and that the victim and suspect were roommates who shared a trailer.
On Tuesday, El Monte police responded to a "suspicious circumstance" call in the 3300 block of Maxson Road at approximately 10:25 a.m. after the caller indicated a man was dragging a female body toward the dumpsters, the Los Angeles County Sheriff's Department said in a news release.
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It is believed surveillance video released shows a man pushing a container with the woman's body inside.
The body was later found inside a dumpster by El Monte police, authorities said.
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The victim's cause of death is unknown.
Anyone with information is asked to contact the Los Angeles County Sheriff's Department Homicide Bureau at (323) 890-5500.