Police tape is pictured at the site of a fatal stabbing at the Champlain Valley Fairgrounds on Monday morning. (Photo by Kaylee Sullivan)

Police tape is pictured at the site of a fatal stabbing at the Champlain Valley Fairgrounds on Monday morning. (Photo by Kaylee Sullivan)

UPDATE: Essex police have arrested stabbing suspect Jacob St. Amour in Williston.

Essex Police say a South Burlington man was stabbed to death at the Champlain Valley Fair late last night.

Police were actively searching for 20-year-old suspect Jacob St. Amour of Williston. The threat to the public was unknown, Essex Lt. Ken Beaulieu said.

Ryan Durkin, 22, was fatally wounded just after 11 p.m. on Sunday and was pronounced dead at the hospital, Beaulieu said.

Police are searching for Jacob St. Amour, 20, who they say fatally stabbed a man at the fair Sunday night. (Photo courtesy of EPD)

Police have arrested Jacob St. Amour, 20, who they say fatally stabbed a man at the fair Sunday night. (Photo courtesy of EPD)

The victim and suspect knew each other, police said, noting the stabbing was not a random act. The circumstances leading up to the fight are still under investigation. Vermont State Police and other local agencies are assisting Essex PD, a press release said.

Lt. Ken Beaulieu addresses the media Monday morning at Essex Police Department.

Lt. Ken Beaulieu addresses the media Monday morning at Essex Police Department. (Photo by Michaela Halnon)

Police have interviewed several witnesses about the confrontation. Beaulieu was not familiar with St. Amour’s past criminal record.

Sunday marked the final night of the 10-day fair. Essex officers are responsible for policing the event, though the department does hire part-time help from outside agencies, Beaulieu said.

“This is a major case,” Beaulieu said Monday morning. “The fact that it happened on the fairgrounds doesn’t add or detract from that.”

Police expect to release more information later this afternoon. Stay tuned for updates to our story.

Police ask anyone with information to call 878-8331.