Shia LaBeouf‘s alleged stalker told cops she believed the actor was merely a clone of himself … and she feared he was being sex trafficked.

Sources tell TMZ … Alyssa Couture was arrested on July 13 in New Orleans after she allegedly followed Shia to a bank parking lot, where he was with his girlfriend … and when she was being questioned by police, she made some pretty alarming statements.

A source said Alyssa remained across the street from the bank and was seen pacing around her car while Shia was inside the bank. She claimed she was trying to close the “demon portal.”

Cops arrested Alyssa after talking to her. She told officers that the celebrity Shia LaBeouf was a clone that has Shia’s DNA and her DNA mixed together. Alyssa claimed Shia’s clone was made in a secret lab.

Sources tell TMZ … polices first encountered Alyssa on June 30 after she traveled from New Hampshire to New Orleans. When questioned, she said she believed she was married to Shia.

A little over a week later, on July 9, Alyssa showed up at Shia’s father’s home, accusing him of hiding Shia’s real body. She said the clone of Shia was the celebrity Shia LaBeouf, not the real Shia.

Alyssa also claimed she drove to Shia’s California home … due to multiple women committing sex acts on Shia’s clone, which made Shia angry.

And, get this … Alyssa said she felt Shia’s clone was being sex trafficked … and that Shia’s father’s social media posts talked to her through A.I.