The army said the youth was shot after soldiers were attacked with rocks by Arabs who ignored orders to disperse.
Residents themselves attacked looters with rocks and pipes at a food warehouse.
An army spokeswoman said troops in Nablus opened fire after a crowd attacked them with rocks and building blocks.
"Their car was blocked by burning tires, and a group of rioters began to attack them with rocks at close range."
This then began a riot, the French were attacked first with rocks, then weapons, killing them all.
The next day, large groups of workers stopped working and attacked police with rocks and guns.
The investigation concluded that around 500 protesters had surrounded six police officers and attacked them with rocks.
"The army was trying to clear a roadblock, when they were attacked with rocks, stones and bottles," the spokesman said.
The old cultural center was closed in May 1989 after being attacked with rocks and firebombs nearly 30 times over 10 years.
On Jan. 31, prisoners there rioted, and attacked guards with rocks.