But when the time came to go home, she thought the baby she was given looked different, with a darker complexion.

There was a good reason for her confusion: It wasn't her child.

Three months later, TV news cameras captured Casanella and her husband reconnecting with their own son -- a reunion that came after a wide-ranging investigation involving prosecutors, doctors, police and DNA experts.

At the same time Monday night in the El Salvadoran capital, the infant boy that Casanella and her husband, Richard Cushworth, had taken was reunited with his own birth parents.

This roller coaster of emotions started in May on a high when Cushworth, who is British, and Casanella, who is from El Salvador, welcomed their son Jacob into the world.

The couple, who live in Dallas, said Jacob's skin coloring had resembled that of his lighter-skinned father. That's unlike the baby given to them by hospital staffers, who told them that the color change was natural and nothing to worry about.

Separated at birth, reunited on Facebook

But that explanation didn't satisfy Casanella and Cushworth, who took their suspicions to authorities.

Salvadoran prosecutors found out there had been four babies born at the same hospital the day Casanella gave birth. They ordered DNA tests for all of them.

Dr. Josefina Morales de Monterrosa, from the Legal Medicine Institute of El Salvador, was in charge of conducting the tests. She said that when the DNA sample of a baby given to another couple was compared with that of Cushworth's and Casanella, there was a match.

"We obtained absolute compatibility with a 99.9999 probability, which means that the paternity and maternity are practically proven," Morales said. "This is the highest index of probability of paternity in these type of cases."

How did the babies get switched?

Authorities are trying to figure out exactly how and why this happened.

Already, police have arrested Dr. Alejandro Guidos, the gynecologist who delivered baby Jacob by C-section. Guidos claims that he's innocent of any wrongdoing. He was released on bond, but authorities have ordered him not to leave El Salvador.

The mix-up also spurred Salvadoran authorities to order a review of protocols followed at public and private hospitals in the country to prevent this again.

Still, while the case triggered investigations, it also spurred introspection and celebration.

"In this case, we never had to use a sword," Martínez said. "We utilized the strength of truth, justice and all of our capacity to clarify this dramatic and unique situation in the history of our country."

The other family involved has chosen not to speak about the case publicly. Authorities are withholding their identities to respect their wishes and to protect the rights of their baby.

Yet Cushworth and Casanella have spoken out. Most recently, they focused not on their months-long struggle but their happy reunion as well as their gratitude for their family members and friends back home in Texas.

"There are no words to express what our heart feels to have our baby at home!" the couple said in a statement. "Thanks to all who joined our pain and fed our hope."

CNN's Greg Botelho, Laura Perez Maestro and Archith Seshadri contributed to this report.