Questions remain as to whether the dead newborn was born in the bathroom or if the body was placed there.
The infant was found inside a bag which had been stuffed into the rubbish inside a women's toilet at the site in Pheonix, Arizona.
The baby was treated by emergency workers but was said to be "beyond resuscitation".
Fire officials later confirmed the infant had died.
Police have located the child's mother and spoken with her, a police spokesperson said, but have released no information about her identity, including whether or not she is an Amazon employee.More news: Fourth seed Zverev scrapes into Australian Open third round
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Images taken late last night show that the building was cordoned off and that the authorities were still at the scene of the tragedy.
In a statement, an Amazon spokesman declared, "This is a terribly sad and tragic incident. The safety and wellness of our team is our top priority", said Amazon spokeswoman Lauren Lynch.
The warehouse continued its operations while officers investigated.
Authorities said the investigation into the baby's death is ongoing.
An Arizona law passed in 2001 allows mothers to leave their newborns with someone at a safe-haven facility without fear of prosecution.