A Florida couple has been arrested and charged after an elaborate plan to kidnap a baby girl in Washington state, officials said.

Marryl Ardila-Urrego, 33, and Chun Ho Vincent Lai, 42, were arrested after they were pulled over on Interstate 90 about three hours after kidnapping a 7-month-old baby and injuring her mother on Feb. 20, according to court documents filed last week and reviewed by USA TODAY.

"This case is extraordinarily unusual. The defendants live in Florida and apparently came to Washington solely to commit this crime," King County Senior Deputy Prosecutor Jennifer Phillips wrote in the charging documents.

The pair were charged with first-degree kidnapping, first-degree robbery, first-degree burglary, second-degree assault of a child, and second-degree assault.

Mother was related to one of the suspects

According to the charging documents, the child's mother was Ardila-Urrego's cousin. Ardila-Urrego told the mother that she had ordered a bed frame for the baby's 2-year-old sibling that would arrive from Amazon on Feb. 20.

The mother and her family had just moved into their home in Federal Way, Washington, about 20 miles south of Seattle, approximately a week before the incident. According to the charging documents, on the morning of Feb. 20, after her husband left for work, the mother heard the doorbell ring. When she went to see who it was, she spotted a man dressed in a jacket and sunglasses, and holding an Amazon box and clipboard at the door.

When she opened the door, the man, who prosecutors identified as Lai punched her multiple times before forcing his way into the house.

Lai knocked the mother to the ground and bound her wrists and ankles with zip ties. Then a woman, who officials identified as Ardila-Urrego walked into the house and held the mother down, as Lai went to search for and grab the 7-month-old baby, who he then placed in the Amazon box.

According to probable cause documents Lai gestured to the mother that he would stab the 2-year-old if she did not cooperate.

Lai gagged the mother and threw her and her 2-year-old into a bedroom, closed it, and left, the documents said.

License plate, cell phone used to track suspects

By the time, the mother was able to free herself, she realized her baby was gone. She and her 2-year-old ran outside, where maintenance workers removed the remaining zip-ties and neighbors called 911.

"It is shocking the level of disregard for the safety of the 7-month-old baby and 2-year-old toddler and their mother that these defendants displayed by their actions," Phillips wrote in the charging documents.

Police reviewed surveillance footage that showed the pair parked a white sedan near the home. Investigators also spoke with the child's grandfather, who told them he believed his niece, Ardila-Urrego, could be involved.

The grandfather told FBI agents that Ardila-Urrego had been persistently asking for his daughter’s address, even though she was not close to them.

The FBI then used Ardila-Urrego’s cellphone and an automated license-plate reader to track the pair, according to the legal documents. That information was then relayed to State Patrol officers, who conducted the traffic stop of Lai's car. The pair were found about 180 miles east of where the child was taken from.

Baby safely returned to family

The baby was found safe and returned to her family, according to the documents.

Officials have not identified a clear motive for the abduction, but said there is "no evidence that mental illness or substance abuse contributed to this crime and it appears that the victims were targeted because they were known to the defendants and known to have children."

Ardila-Urrego and Lai are both being held on $750,000 bail and are scheduled to be arraigned on March 7.

Sarah Al-Arshani covers breaking and trending news for USA TODAY. Reach her at [email protected].