Tyler James Peterson was born on March 6, 1987, and grew up in Crandon. He graduated from Crandon High School in 2005 and was hired as a full-time deputy in the Forest County Sheriff's Department on September 11, 2006, also serving part-time with the Crandon Police Department. He had dated 18-year-old Jordanne Michele Murray for four years before their relationship ended the month before the shooting. On that October night, Peterson arrived at the duplex where Murray and six others were gathered. He argued with the group, then returned to his car. He came back with his AR-15 style rifle and kicked down the door.

Peterson fired approximately 30 rounds from his rifle as he moved through the duplex. He killed three people in the living room, one in the kitchen, one outside a closet, and one who had tried to hide inside a closet. The youngest victim, Lindsey Stahl, was just 14 years old. The oldest, Charlie Neitzel, was 21. Neitzel fell in the kitchen after being hit and pleaded with Peterson to stop. He tried to grab the rifle. Peterson shot him a second time, and when Neitzel played dead, shot him a third time. Neitzel survived. Six others did not: Aaron Smith and Bradley Schultz, both 20; Jordanne Murray, 18; Katrina McCorkle and Lianna Thomas, both 17; and Lindsey Stahl, 14. Every victim was either a student or recent graduate of Crandon High School.

Leaving the duplex, Peterson encountered officer Greg Carter driving toward the scene. Carter did not initially suspect his fellow officer. Peterson sprayed the windshield with gunfire, wounding Carter with flying glass. Carter threw himself sideways and reversed away. Peterson fled into the night, calling in false reports of his own location to misdirect the response. Hours later, authorities tracked him to a friend's cabin seven miles north in Argonne, where he had taken hostages. At 12:30 p.m., Peterson attempted to escape into the surrounding woods. A police sniper struck him in the left arm. Peterson then turned his Glock pistol on himself, firing three times. His death was initially attributed to the sniper, but investigators later determined the fatal wounds were self-inflicted.

Charlie Neitzel, the sole survivor, was discharged from the hospital on October 17, 2007, ten days after the shooting. The duplex where the murders occurred was demolished in June 2008, the community choosing to erase the physical reminder. Families of the victims sued the city, arguing that Crandon had been negligent in giving Peterson access to weapons without requiring a mental health assessment. A judge dismissed the lawsuit and ordered the families to pay $21,000 in legal fees -- a ruling that added a bitter footnote to an already devastating chapter. The incident was later retroactively identified by Mother Jones as the first mass shooting in the United States involving an AR-15 style rifle, a weapon type that would go on to appear in mass shootings at increasing rates in the years that followed.