Eleven people were stabbed over the weekend at a Walmart in Michigan, in what authorities are calling a random and unprovoked attack.

The Grand Traverse County Sheriff’s Office said a 42-year-old man entered the store around 4:45 PM and used a folding knife to stab 11 people before being taken into custody. A sheriff’s deputy arrived within minutes, with help from bystanders in subduing the suspect and aiding the victims.

Munson Healthcare confirmed all 11 victims were being treated at its regional hospital. Six were listed in critical condition, and five were in serious condition. The Sheriff said the suspect is believed to be a Michigan resident. The weapon used appeared to be a folding knife.

The FBI is assisting in the investigation. Walmart said in a statement, “Violence like this is unacceptable. Our thoughts are with those who were injured, and we’re thankful for the swift action of law enforcement and emergency personnel.”