Israeli Prime Minister Benjamin Netanyahu condemned the attack and vowed deal with the "reprehensible murderer" to "the fullest extent of the law".
Conricus identified the gunman as a 23-year-old Palestinian from a West Bank village and said he was still at large. Another woman in her 50s was seriously wounded. He said it appeared to be a "lone-wolf attack" and that security forces were searching for the suspected perpetrator.
The IDF said several people including members of Na'alwa's family were apprehended late Monday and questioned by the Shin Bet security service to determine whether they had helped Na'alwa either carry out the attack or flee the scene.
Ashraf Walid Suleiman Na'alowa from the village of Shweika near Tulkarem entered the industrial park on Sunday morning, shooting two Israelis and severely wounding a third using a locally produced knockoff of the Swedish Carl Gustav sub-machine gun.
Israeli media reported that those killed were found shot to death on their office floor with their hands bound. The Palestinian economy is heavily restricted under Israeli military rule, forcing tens of thousands of Palestinians to seek work in Israel as well as Jewish settlements.
Conricus called it a terrorist attack but said other unspecified factors were involved.
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Mr Varadkar is also due to meet the chair of the European Parliament's Brexit Steering Group, Guy Verhofstadt. Much further-reaching on trade, on internal security and on foreign policy cooperation.
"This was a serious terrorist attack", the military said in a statement.
Moshe Lev-Ran, an export manager at a company whose factory is located next to the scene of the attack, said he doubted the official account. "That's what I think happened".
Palestinians often face tough choices in finding employment in the economically struggling West Bank and jobs in Israeli settlements can provide steady income.
A wave of Palestinian attacks against Israelis broke out in 2015, but they have since become sporadic.