Hospital shooting and death
On 5 December 2017, Fredrik entered the hospital with a hunting rifle and shut off the main power generator in the basement. At the bottom of the staircase, he shot Jac Naylor in the back (HC: "Group Animal - Part One") and made his way towards AAU, where he mortally wounded Raf Di Lucca in a lift. After searching the darkened ward, Fredrik travelled up to Darwin and shot Oliver Valentine in the head as he was operating on a patient.
On Keller, as Fredrik attempted to forcibly enter the theatre where Dominic was hiding the ward's patients, Hanssen confronted him. Once an armed police unit arrived at the scene, Hanssen attempted to negotiate with his son, but Fredrik asserted that he did not want anything from him anymore and loudly declared that he would decide how the situation ended. As the two began sizing each other up, with Fredrik asserting that Hanssen was not a part of the hospital's "family" and proclaiming that he was there to "end it", the police shot Fredrik in the chest, instantly killing him. A hysterical Hanssen, desperate to save his son, rushed Fredrik into theatre and demanded the lifts be turned back on, but he eventually realised that Fredrik was dead and wept. (HC: "Group Animal - Part Two")
Behind the scenes
During series 15 of Holby City, Fredrik was portrayed by an unknown actor in photographs and in the flesh; he made one lineless appearance in "Like a Prayer", the final episode in the series. Fredrik made a return in 2017 during the show's 19th series and was portrayed by Billy Postlethwaite.