Magen David Adom emergency medical services said their medics had entered a building at Barkan where they found a man and a woman without pulse, and pronounced them dead.
Israel's military said it was treating the killings as a terrorist attack.
He shot another woman in the stomach, moderately wounding her. Closed-circuit footage from the scene showed a man holding a handgun and wearing a backpack, fleeing down a flight of stairs and then dashing past stunned onlookers.
The Israel Defense Forces (IDF) identified the fugitive gunman on Sunday evening as Ashraf Waleed Suliman Na'alwa from the northern West Bank village of Shuweika, near Tulkarem.
Troops had searched his house and surveyed it in preparation for demolition, and detained for questioning several Palestinians suspected of assisting him, the IDF added.
"There will be no security for anyone as long as the Palestinian people are denied their rights", the group said in a statement.More news: Dortmund Teenager Sancho Gets England Squad Call
Among those detained were Na'alwa's brother and sister, the Shin Bet confirmed. But other workers in the industrial zone suggested the attack was carried out by a disgruntled employee and was not politically motivated.
The Palestinian militant group Hamas praised the attack, saying it was a "natural response to the crimes of the Israeli occupation", but it did not claim to be behind it.
"One of the workers was sacked and he didn't like the owner".
Palestinians celebrated the horrific execution-style slaying earlier in the day of a young Israeli mother and father.
Israel settlements are considered illegal under global law and major stumbling blocks to peace as they are built on land the Palestinians see as part of their future state.
Last month, a Palestinian teenager stabbed an Israeli to death at a junction at the entrance to a large bloc of Israeli settlements in the West Bank near Jerusalem. Most have been assailants, Israel says.