Law enforcement and medical experts are gravely concerned about the health of 11-year-old Emily Bracamontes, who was removed last week by her mother from a Phoenix hospital where she was receiving chemotherapy treatments for her leukemia, ABC News reports.

Emily's father, Luis, 46, was stopped at the U.S. border over the weekend. Luis was on his own and told authorities that his daughter is receiving care in the family's native country, Mexico. He denied knowing her whereabouts, however.

After undergoing chemotherapy for a month, Emily had her arm amputated to ward off an infection. Since then, she's had a tube in her chest delivering medicine to her heart. The girl's mother unhooked the girl's tube and IV when removing her from Phoenix Children's Hospital last week. 

Police have considered bringing neglect charges against the girl's mother and father. Doctors are especially concerned that Emily could suffer a deadly infection if she isn't promptly returned to treatment. 

"If bacteria get into the blood stream, that can cause a serious infection," Dr. William Schaffner, an infectious diseases specialist at Vanderbilt University Medical Center, told ABC News. Schaffner says the open catheter is essentially an alleyway for bacteria that could kill Emily. 

In interviews, Luis Bracamontes admitted that the family bolted because it blamed the hospital for losing Emily's arm and couldn't pay her mounting medical bills. 

Police and hospital staff say that first and foremost, their concern is for Emily's safety, not unpaid medical bills. 

"We understand the right of a parent to change doctors, to change hospitals, we're not challenging that," Phoenix Police Sgt. Steve Martos said. "We just want to make sure that Emily is getting the right medical attention that she requires to prevent this potential horrific ending."

A hospital spokesperson added that they're more than willing to discuss Emily's care with her family. 

Martos and law enforcement are perplexed as to why the girl's family won't provide them basic information about her whereabouts. In addition to Luis Bracamontes, who denies all knowledge of his daughter's location, her grandfather, also named Luis Bracamontes, said he has not spoken to his son and does not know where his granddaughter is. 

"We are worried because we don't know what's going on," said Bracamontes, 76, in Spanish from his home in San Jose, Calif.

"Martos says the department won't stop looking for Emily, even if she's been taken out of the country. "We can't just drop it," he said.