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The Dallas hospital that mistakenly sent home a man who had Ebola says flawed software and not human error caused doctors to miss the diagnosis.

Health officials and local residents have been asking how the hospital could have missed what would have appeared to be an obvious potential case of Ebola: a Liberian citizen who said he recently traveled from Liberia, with fever and abdominal pain.

“Protocols were followed by both the physician and the nurses,” the hospital said in a statement issued Thursday night.

The nurse who took Thomas Eric Duncan’s medical history did the job correctly, the hospital said.

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“However, we have identified a flaw in the way the physician and nursing portions of our electronic health records (EHR) interacted in this specific case,” it added.

“In our electronic health records, there are separate physician and nursing workflows. The documentation of the travel history was located in the nursing workflow portion of the EHR, and was designed to provide a high reliability nursing process to allow for the administration of influenza vaccine under a physician-delegated standing order. As designed, the travel history would not automatically appear in the physician's standard workflow.”

In other words, the nurse wrote that Duncan had come from Liberia, but the doctors who examined him would not have automatically seen that. And they were not prompted to ask.

“As result of this discovery, Texas Health Dallas has relocated the travel history documentation to a portion of the EHR that is part of both workflows. It also has been modified to specifically reference Ebola-endemic regions in Africa,” the hospital said.

“We have made this change to increase the visibility and documentation of the travel question in order to alert all providers. We feel that this change will improve the early identification of patients who may be at risk for communicable diseases, including Ebola.”

The hospital also gave more detail about Duncan, who traveled from Monrovia to Dallas Sept. 19 and who started feeling ill Sept. 24. He first sought care on Sept. 26.

“Mr. Duncan presented with a temperature of 100.1F, abdominal pain for two days, a sharp headache, and decreased urination. These symptoms could be associated with many communicable diseases, as well as many other types of illness. When he was asked whether he had nausea, vomiting, or diarrhea, he said no. Additionally, Mr. Duncan’s symptoms were not severe at the time he first visited the hospital emergency department,” the hospital said.

"When Mr. Duncan was asked if he had been around anyone who had been ill, he said that he had not."

“When Mr. Duncan was asked if he had been around anyone who had been ill, he said that he had not,” it added.

NBC News has interviewed a taxi driver and other witnesses who say Duncan traveled in the taxi with a pregnant woman who appeared to be miscarrying and who later died of Ebola. They said Duncan helped her.