BALSAM LAKE, WIS. – The late revelation of a prosecution strategy threatens to sink a Minnesota man's defense against homicide charges in the killing of a fellow fisherman.

Levi Acre-Kendall, 20, of Cambridge, Minn., is claiming self-defense in the April 14 stabbing death of St. Croix Falls, Wis., resident Peter S. Kelly. He's hoping jurors will find his actions justified under Wisconsin's "castle doctrine," which protects people using deadly force against someone they believe has unlawfully entered their house, business or vehicle while presenting imminent threat of bodily harm or death.

But the law doesn't apply if the person using force is already engaged in illegal activity. On Tuesday, the second day of Acre-Kendall's trial in Polk County Circuit Court in Balsam Lake, it was revealed that the prosecution believes Acre-Kendall used a knife illegal in Wisconsin to kill Kelly — a switchblade.

Acre-Kendall faces one count each of first-degree reckless homicide and second-degree intentional homicide.

Acre-Kendall's attorneys, Eric Nelson and Doug Hazelton, said they weren't made aware of the prosecution's stance on the knife until a talk Friday with Polk County District Attorney Dan Steffen.

Nelson said the issue was "very complicated," and came as a surprise since the trial began Monday. The knife is legal in Minnesota, Nelson said, and was legally purchased there. He raised other legal and constitutional concerns.

Ross Lechman testified that he attempted to stop the bleeding from his close friend Peter Kelly's chest wound with his hands until EMS arrived.

Tuesday's discussion occurred outside the hearing of jurors.

Steffen took issue with Nelson's claim, noting that the defense had access to the knife in preparation for trial.

"This was not a surprise," Steffen said.

Judge Molly GaleWyrick jumped in: "I'll tell you what — I was surprised."

The judge said she was first informed of the issue on Monday, and that both sides bore responsibility for the delay.

Nelson argued that the knife was a "spring-assisted" knife. Steffen called it a switchblade.

GaleWyrick ruled that Steffen could not refer to it in court as a "switchblade" or an "illegal knife," but that he could have witnesses demonstrate a push-button function that caused the blade to sweep out sideways from its handle.

Despite that, the judge noted, it would be "more difficult" for the defense to argue the castle doctrine.

Kelly, a married father of five, was stabbed about 9:30 p.m. after he and his best friend, Ross Lechman, became engaged in a dispute with Acre-Kendall and his friends as the two groups fished 600 feet apart on opposite shores of the St. Croix River.

Kelly and Lechman, who each had had four alcoholic cider drinks that night, were fishing on the Minnesota side of Interstate Park. They grew upset with the swearing and alleged marijuana use from Acre-Kendall's group on the Wisconsin side.

Kelly, whose blood alcohol content tested at .043, and Lechman drove over to confront Acre-Kendall and his three friends. Lechman testified Monday that he shoved Acre-Kendall to the ground, and that Kelly was later stabbed.

Acre-Kendall's friend, Jacob Mossberg, testified Tuesday that after he was pushed, Acre-Kendall brandished a knife and retreated to a friend's car, but Kelly pursued him.

Chao Xiong • 612-270-4708 Twitter: @ChaoStrib