The armed man gave himself up early on Saturday after some seven hours of negotiations with authorities.
“This man entered the jewelry store but there was no attempted robbery and his motive is not known,” said prosecutor Christophe Barret.
The hostage taking caused anti-terrorist police to block off a large part of the city’s center.
Barret added that the incident had no link to the recent attacks around the capital Paris.
On Friday, two brothers, Said and Cherif Kouachi, suspected of slaughtering 12 people two days earlier at the Paris office of Charlie Hebdo satirical weekly, were killed after being cornered at a printing workshop with a hostage in the town of Dammartin-en-Goele, northeast of Paris. The two had earlier released the hostage.
On the same day, police ended a second hostage-taking in a supermarket in the eastern Porte de Vincennes area of Paris, killing one armed hostage-taker, Amedy Coulibaly, who was a suspect in killing a policewoman in southern Paris a day earlier. Officials say four hostages were also killed during the raid.
The ISIL Takfiri group has claimed responsibility for the attacks, threatening to target the United States and Britain next.
French police and intelligence services have been facing mounting criticism over their lack of intervention before the attack on Charlie Hebdo newspaper headquarters.
One of the main suspects of the Wednesday attack had reportedly been convicted on terrorism charges and another is thought to have had links to Yemeni al-Qaeda militants.