The 55-year-old woman, who has been named as Concha M. N, was discovered in an "unfrequented" area of the cinema in Valencia, on Spain's east coast, on Tuesday.
She may have "passed out, fallen and died" when she went to see a film on April 12th, seven days before she was discovered, said the representative of the regional Valencian government, Juan Carlos Moragues.
The woman’s body was discovered by a cleaner "between two emergency doors, where there are some stairs" Moragues confirmed, referring to an underground area of the ABCPark cinema in Valencia.
The cleaner noticed a "strong smell" and when she opened the door she found the body in an advanced stage of decomposition. Alongside the body the cleaner found a bag and a pair of glasses.
The woman was reported missing by her husband on Wednesday, April 13th.
"We suspect that she has been dead for one week. There were some bloodstains on the stairs. She could have fainted, fallen and died at this moment," he said.
An autopsy was due to be carried out on Wednesday to determine the cause of the woman’s death. Sources close to the investiagation told local newspaper Levante that the woman's death was caused by a fall down the stairs.