A couple discovered the child they were babysitting was actually the victim of an abduction after seeing a missing persons alert on Facebook.
John Truong and his wife were looking after two-year-old Ronnie Tran who was taken from his home in Des Moines, Washington.
John told authorities his sister Alyssa Chang had asked him if he and his wife could watch who she said was her 'boyfriend's son' on Tuesday night.
The sister said she and her boyfriend were planning an overnight date and she would return to collect the toddler on Wednesday morning.
John and his wife babysat the child and then handed him back as arranged.
But later that day, he saw an alert for the boy on Facebook, saying he was missing, and he immediately called police.
Detectives then went to the boy's home and found him safe, sound and unhurt.
In an extraordinarily complex saga, police said Chang and the child's paternal grandmother, Vien Nguyen, had gone to the boy's home on Tuesday and zapped his mother with a Taser then locked her in a garage. Chang then took the boy to her brother's house to look after overnight.
The mother then freed herself and raised the alarm - leading to the missing persons alert for her son.
Police arrested the sister on charges of kidnapping, assault and unlawful imprisonment and she is being held on $250,000 bail. The grandmother is also being questioned by authorities.
But the motives for the bizarre crime are baffling and unclear, say police.
Mr Truong told KOMO news: "I'm eating my breakfast, I'm checking my Facebook, all of a sudden I see this Amber Alert for this child.
"And it looks like this child in my bed, and I'm like, 'Oh my God! What's going on?'"
He said the boy appeared fine the night before, enjoying a quiet night in watching movies and eating popcorn.
John added: "He was a great kid. He didn't cry much or anything. He enjoyed my dog's company and my children's company."
He said he was completely taken aback by his sister's arrest in the bizarre kidnapping.
He said: "I feel like she was just helping her boyfriend out and just got into this horrible situation.
"We're family people, this is definitely not like this. Honestly I'm at a loss for words right now. It's just crazy."
Detectives have yet to reveal a motive for the crime.
Sgt Mike Graddon of the Des Moines Police told King 5: "Our detectives are currently investigating this case.
"It's very, very complex, and that is all the information we have at this point, but Ronnie has been found."
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