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Sex Contracts and Wooden Boxes: A Brief History of Swedish Kidnappings

Kidnappings are very uncommon in Sweden, but they are usually pretty fucked up when they occur.
From the Swedish Police preliminary investigations of the Martin Trenneborg case.

Kidnappings might not be that common in Sweden, but when they do happen they are pretty fucked up. So much so that a peculiar phenomenon which sometimes appears in conjunction with kidnappings – where hostages develop positive feelings toward their captors – has been named after a hostage situation that took place in Stockholm in the 1970s.

The latest kidnapping to take place in Sweden was made public in September 2015. On the evening of the 18th, 37-year-old Martin Trenneborg entered a police station in central Stockholm alongside a woman in her early thirties. After briefly speaking to the receptionist, the pair sat down in the waiting hall. Two hours later, the woman was called into an interrogation room. The man stayed in his seat. Then four police officers came out and arrested him, marking the climax of a disturbing news story that the tabloids dubbed "The Sex Bunker Doctor" and "Swedish Fritzl". The chain of events includes a sound-proof bunker, poisoned strawberries and a sex contract. But more on all that latter.


On the 23rd of February, a Swedish court sentenced Trenneborg to 10 years in jail for kidnapping. Ever since the story broke, several criminology experts have stated that this case is one of the most disturbing in Swedish criminal history. In recognition of this alarming milestone, we assembled a brief history of Swedish kidnappings.

A newspaper picture of Ann-Marie and a police officer in 1963, reposted by Gävledraget.

The Gevalia Daughter

The first case of kidnapping in modern times took place in 1963 – at least as far as we know. Ann-Marie Engwall, the 7-year-old daughter of Jacob Engwall, Managing Director of Gevalia (Europe's largest coffee roasting company at the time) was abducted on her way to school. The kidnappers, a man and and woman who remained anonymous, claimed they were going to drive her to a school trip she had just missed.

To pass the time while waiting for the ransom money (a sum of about €1,500 which they apparently needed to fund their own private detective agency), the perpetrators took Ann-Marie to a petting zoo and to a café. As soon as the ransom was collected, the kidnappers put Ann-Marie in a taxi to be sent to her parents. Not wanting to go by herself, and unable to grasp the concept of abduction, she tearfully asked the kidnappers to join her.

Mr. and Mrs. Engwall contacted the police right after their daughter arrived. The kidnappers turned themselves in that same day. They would do rather well later in life, however. Once they served their sentences, they got married, and had successful careers within governmental organisations.

The Girl in the Box

The kidnapping of Swedish Olympic equestrian Ulrika Bidegård took place in 1993. Swedish carpenter Lars Nilsson who had worked on renovating the Bidegård family home attacked her outside her parents' house in Belgium. He tied her, gagged her and sedated her with paint thinner. On the way up the stairs to his apartment in Brussels, he dropped Bidegård on her face, busting her lip. Once inside, she was forced to wear a blindfold, noise-cancelling headphones and was tied sitting up inside a homemade, wooden port-a-potty. During the four days she was held captive, she was given little food and water and was constantly uncomfortable.


Belgian police managed to locate Nilsson after he used Bidegård's credit card to make cash withdrawals. They raided his apartment two days later, arrested him and liberated Bidegård from her wooden prison.

A ransom letter arrived at the Bidegård estate the day after Nilsson's arrest, enclosed with a photograph of Ulrika inside the box, demanding $500,000. During the investigation, people close to Nilsson described him as kind and sound, without criminal inclinations.

The Westerberg Case

In 2002, a man posing as a flower deliveryman kidnapped Erik Westerberg, son to a successful business executive, from his home in Stockholm. Westerberg had been featured at the top of a list of wealthy youths, which was published in an evening paper that same year. Westerberg was also put in a box, and then transported to a cottage on an island outside of Stockholm where he was chained to a bed.

The kidnappers demanded for about €1,000,000 in cash to attached to a wire under a bridge outside of Paris, France. Westerberg's father delivered the money personally. Soon thereafter, the kidnappers released Erik and gave him a pack of cigarettes and some matches. The Swedish Task Force found him after he had smoked about three cigarettes. Once his identity had been confirmed, Swedish police notified their colleagues in France and shortly afterwards, French police arrested the two accomplices that had received the ransom.

The box where Fabian Bengtsson was held. Photo: Swedish Police

Another Man, Another Box


The box is a recurring theme in Swedish kidnappings. On the morning of February 3rd, 2005, Fabian Bengtsson was found in a park in Gothenburg, having just been released by his abductors after 17 days in captivity. "Start walking, you are free, don't look back" was the last thing the kidnappers told him before they let him go.

Bengtsson, heir to SIBA, one of the leading Nordic chains for consumer electronics, was attacked with teargas in his garage, crammed into an empty TV-box and brought to some kind of hovel. Once there, he was transferred to another, more luxurious, soundproof, wooden box with a mattress inside. The kidnappers had targeted him in an attempt to extort about €5,000,000 from the Bengtsson family.

Over time, however, the kidnappers grew to like the abductee. When they weren't threatening him with a homemade gun or shoving balls of tape into his mouth, they cooked him omelettes and washed his clothes; drank whiskey and played cards with him. After a little more than two weeks, overtaken by sympathy, they released Bengtsson. They were caught by the police thanks to the many mental notes Bengtsson took while in captivity; like at what hours he heard the sound of the ice-cream truck turn the corner onto their street, and how long it took the kidnappers to get food from McDonald's.

The unheated basement where Åhman was held captive. Photo courtesy of Swedish Police

Bad Students


Alexander Åhman, another son of another wealthy businessman, disappeared from his student flat in Uppsala a few days after Christmas in 2011. His abductees were his housemate, a psychology student, her presumed boyfriend who was a medicine student, and one more of their friends. After the flatmate had treated Åhman to a pie containing sedatives (the pie was bitter apparently, but he ate it anyway to be polite) the kidnappers taped him up, put him in the back of a van and drove 570 kilometres to an abandoned school building in the city of Umeå.

Åhman spent his week in captivity in a dark, unheated basement, with very little food – beer being his only source of nutrition by the end – and only a thin mattress to sleep on. It was very cold, so Åhman tied diapers he found in the room to his feet to retain some warmth.

Four days after the kidnapping, two of the kidnappers were in the vicinity of Stockholm. The pair had taken Åhman's mobile phone in order to text his family, posing as him. With the app "Find My iPhone", the family traced the phone, noting it moving North on the highway. The police caught the kidnappers with the help of the app, and Åhman was rescued two days later.

The image above is the copy of a sex contract found in a folder called "Master Plan" on Trenneborg's computer. It made headlines due to its deviant and sadistic nature.

The Sex Bunker Doctor

Some time in 2010, Dr. Martin Trenneborg allegedly began building a faux machine shed next to his country home, in Knislinge in Southern Sweden. Inside the shed he constructed a 60 square meter, sound proof, concrete bunker with double security doors equipped with electronic locks.


Five years later, in September 2015 to be precise, Dr. Trenneborg is on a date with a woman, in her apartment in Stockholm – 550 kilometers from Knislinge. He stays for two hours, during which they chat and have sex, and then he suggests that they meet again in two days. She accepts. He goes back to Knislinge that same evening to prepare.

On their second date they drink champagne and he feeds her Rohypnol-laced strawberries. Once she's intoxicated beyond comprehension, he hands her a diaper which she puts on herself. He then fetches a wheelchair from his car, rolls her out and puts her in the passenger seat. He injects her with sedating drugs on the hour, during the seven-hour drive. The woman's only memory after eating the strawberries is waking up in the car and noticing a heart rate monitor clipped on her finger.

She wakes up in Dr. Trenneborg's bunker. He allegedly says that she's going to stay for a few years, cooking for him, hanging out and having unprotected sex two or three times a day. He takes her blood and vaginal samples so he can test her for STDs, and gives her birth control pills. He also says he's considering abducting another woman to keep her company – possibly her mother.

Five days after the abduction, Trenneborg leaves for Stockholm to pick up a few things from the woman's apartment and to attend a U2 concert. When he comes home the next day, he offers to drive her back to Stockholm to get some of her stuff. At this point, the police has left a note on the woman's apartment door, stating that she is missed by her family and that her locks have been changed by the police.

During the trip to Stockholm, worried that police are on to him he coaches her to pretend that they are a couple. He says he doesn't want to go to jail. The fact that she is being complaisant and has not attempted to escape makes him hopeful she will not rat him out. The pair arrive to the police station in central Stockholm and it's not until she is separated from the man, that she tells the police officers what has happened to her.

On the 23rd of February, Martin Trenneborg was sentenced to ten years in prison for kidnapping. He also has to pay the woman a penalty of €19,000 in damages. Trenneborg admitted to kidnapping her but denied and was acquitted of a rape charge.