A federal jury in Texas on Friday found a Brazilian couple guilty of helping their daughter kidnap a Houston doctor's son and take him to Brazil, where the child remains, but declined to convict them of a related conspiracy charge.

The split verdict came five years into Houston doctor Chris Brann's campaign to retrieve his son Nicolas, now 8, from Brazil, where his ex-wife Marcella Guimaraes took him for a temporary trip in July, 2013 and failed to return.

The child's Brazilian grandparents, Carlos Otavio Guimaraes and Jemima Guimaraes, sat in stunned silence as federal judge announced the verdict, following three and a half days of jury deliberations.

With Brann's permission, their daughter took Nicolas, known as "Nico," to Brazil for a 2013 family wedding and refused to return. She successfully petitioned a Brazilian court that year to grant her sole custody, and enrolled her son in a local Brazilian school.

Brann has said he has spent hundreds of thousands of dollars in an effort to get his son back, and has sought the help of the U.S. State Department, the U.S. Federal Bureau of Investigation (FBI) and the Hague Abduction Convention - a 1988 international agreement that seeks to facilitate the return of children removed in violation of custody agreements from their "habitual residences."

Both the U.S. and Brazil are signatories to that agreement, but in a 2017 report, the State Department said that Brazilian “judicial authorities...persistently failed to regularly implement and comply with the provisions of the Convention.”

Last year, federal prosecutors in Texas filed a criminal complaint seeking the arrests of the grandparents and their daughter, and earlier this year the grandparents were arrested when they arrived at a Miami, Florida airport to attend the birthday party of a different grandchild.

Like his daughter Marcella, Carlos Guimareas is a dual Brazilian-American citizen and holds two passports. He and his wife surrendered their passports to U.S. authorities during an earlier bond hearing.

'If my ex-wife Marcelle returns with Nico to the United States immediately, I will happily appear at the Guimarães' sentencing hearing to advocate maximum leniency.'

Marcella Guimareas - who could not immediately be reached for comment - and Nicolas have remained in Brazil, out of reach of U.S. authorities, since 2013.

Brann told ABC News on Friday that he had mixed emotions about the verdicts.

“I never wanted it to come to this and the only thing I want is for my son to come home," he said. "I hope they will take responsibility for their actions and do everything they can do have him come home as soon as possible.”

The convicted couple will remain under house arrest at the Houston home of their son, Roberto Guimaraes, pending sentencing. They face up to three years in prison.

In a separate statement issued after the split verdict, Brann said that "this is an incredibly sad day for me" and vowed to advocate for a lenient sentence for the grandparents if his son is immediately returned to the U.S.

"Despite all the cruelty they have heaped on my extraordinary son Nico, by obstructing his relationship with me, Nico remains my sole concern.

"If my ex-wife Marcelle returns with Nico to the United States immediately, I will happily appear at the Guimarães' sentencing hearing to advocate maximum leniency."