New reports about the 27-year-old Wisconsin man who went on a killing spree before turning his weapon on himself on Sunday reveal he suffered from major depression.

Officials say that Sergio Valencia del Toro randomly shot and killed three people and wounded another on the Fox Cities Trestle Trail Bridge Sunday evening. The victims were identified as Adam Bentdahl, 31, Jon Stoffel, 33, and Stffel's 11-year-old daughter, Olivia, reports The Associated Press. Stoffel's wife, Erin, 32, survived after being hit with three bullets; however, she is listed in serious condition at Theda Clark Medical Center in Neenah.

On Tuesday, Valencia del Toro's fiancée, Haylie Peterson, 24, told Post-Crescent Media that he was depressed and irrational. She also revealed she had gotten into a heated argument with him at their home in Menasha just hours before he went on a rampage.

After the argument ended around 5 p.m., the couple separated, said Aaron Zemlock, community liaison officer for the Menasha Police Department.

Peterson said she expressed concern to Valencia del Toro about his depression that evening before she left the house so they could both cool off.

"I left because we agreed we both needed time to process our emotions," she told Post-Crescent Media Tuesday.

Police say that's when Valencia del Toro biked to the Trestle Trail, which is about a mile away from their home, carrying two handguns. He opened fire on the bridge around 7:30 p.m., shooting the victims at a close range.

Peterson also released a statement on behalf of her family and Valencia del Toro's family, saying, "The man we loved and knew did not commit this."

"The families of Sergio Valencia del Toro send deepest sympathy to all families and friends traumatized by this tragedy," reads the statement. "We mourn and grieve with you and pray for all affected by this."

Valencia del Toro was studying criminal justice at the University of Wisconsin-Oshkosh. Police say that he was discharged from the U.S. Air Force in 2014 and recently enlisted in the U.S. Army.