Lehnberg's upbringing had been both ultra-conservative and strict. Her father was puritanical, a man who rarely displayed any affection towards his daughters. She had not been allowed to socialise and had never been to the cinema during the time she was in high school, she was a very intelligent young girl academically and often came first in her class but had no experience of boys or men, she was very naive and innocent and tried hard to get attention via her studies. She was drawn to van der Linde, a person whom she saw as a being warm and friendly father figure.
Van der Linde and Lehnberg struck up a father-daughter type relationship which grew closer as the months passed. Eventually, he found her impossible to resist or more likely, he seduced and groomed the young and inexperienced girl. In April 1973, a year after they first met, the couple began an affair.
Despite the fact that Van der Linde had declared that he would never leave his wife and family, Lehnberg was convinced that the only obstacle to them having a more permanent relationship was the presence of Van der Linde's wife, Susanna.
By July 1974, Lehnberg was becoming desperate and started talking about leaving Cape Town. Christiaan van der Linde persuaded her not to, but by September she had finally tired of the situation and decided to bring matters to a head herself by speaking to his wife. She called her and explained that she and Christiaan were very much in love and were seeing each other every night. She wanted to know what Mrs van der Linde intended doing, but Mrs van der Linde hung up on her. A few weeks later, Lehnberg telephoned again. This time she made an appointment to go and see her. They met in Bellville early in October.
Initially, Lehnberg had hoped that she and Mrs van der Linde could come to some sort of arrangement concerning Christiaan, but this meeting was to change all of those ideas. Not only did Mrs van der Linde tell Lehnberg that she would never give her husband a divorce because of the children, she also added, she didn’t mind playing second fiddle as long as Lehnberg didn't mind either. It was obvious to Lehnberg that Susanna van der Linde was prepared to do anything to keep her husband.
Lehnberg first contacted Choegoe by letter, which she wrote to him care of Solly's Trading Store, his local shop. In the letter, she asked him to come and see her at the Orthopaedic Workshop and added that if he were smart he could still earn earn good money. When he turned up at the workshop, Lehnberg gave him R1.00 and asked him to meet her at the Rondebosch town hall at 7 p.m. that evening, where she gave him a bottle of gin and said that she wanted him to murder a woman for her. Choegoe at first declined, saying that he would be sent to the gallows.
After some discussion, Choegoe finally agreed to Lehnberg's request. Several days later, he went to the address in Boston Estate which Lehnberg had given him, claiming that he planned to warn Mrs van der Linde that her life was in danger. Instead of warning Mrs van der Linde of Lehnberg's plans, he asked her for some change. She said she didn't have any and went back inside the house.
A week later, Choegoe and Lehnberg met in Rondebosch once more. This time he admitted that he was too afraid to go through with the murder. Lehnberg promised that she could see to it that he received help with his artificial limb, if he did away with Mrs van der Linde. She also gave him a radio. Choegoe went to Bellville once more. On this occasion, he simply walked past the house but made no attempt to enter.
Shortly afterwards Lehnberg sent Choegoe a second letter. Again she urged him to go through with the murder, using a knife if he had to. Then, she got another message to him, asking him to telephone her at work. During the subsequent conversation, Lehnberg insisted that Choegoe go through with the murder. She promised to give him a car and to have sex with him once the crime had been committed.
In the face of repeated failure, Lehnberg decided to take matters into her own hands again. A few days after Choegoe's failed attempt, she approached Rob Newman (24), an engineering student whom she knew, and asked to borrow his Llama pistol. When he refused, she asked if he would kill someone for her. Again, he refused. On 28 October, Newman's pistol was stolen from his room. He reported the theft to the police and suggested Lehnberg as a likely suspect.
Around 8.30 a.m. on the morning of Monday 4 November 1974, Lehnberg arrived at Choegoe's home. She said that her car was packed and she was on her way to Johannesburg, but before she left she needed Choegoe to come with her to van der Linde's house. He claimed in a statement that it wasn't until she handed him the Llama pistol on the way to Bellville that he realized that she wasn't just going to say goodbye.
They arrived outside the house just after 9 a.m. Mrs van der Linde was alone inside. From this point on, Choegoe's account and Lehnberg's account of what followed, differ.
Choegoe said that after Lehnberg rang the bell, they went into the house together. When Mrs van der Linde saw them both, she became frightened and threatened to phone the police. She attempted to get away, but was tripped by Lehnberg, fell and hit her head on the door. While Mrs van der Linde was on the floor, Lehnberg struck her on the jaw with the pistol butt. On Lehnberg's instructions, Choegoe began to throttle the semi-conscious Mrs van der Linde. Lehnberg then gave him a pair of scissors she had taken from the sideboard. Choegoe said he remembered stabbing her three times. The pathologist noted seven stab wounds, six of which had penetrated the chest.
After the murder, Lehnberg squirted green dye over Choegoe using a gas pistol belonging to Mrs van der Linde. After warning Choegoe that she would deny any involvement in the murder if he went to the police, Lehnberg took him home. She set off for Johannesburg, collecting two speeding tickets at Beaufort West on the journey.
When the police brought van der Linde home, to identify his wife he casually turned the body with his foot and said that it was his wife, this was reported at the time by the police officers present as appearing callous and almost as if he had been expecting it.
It was suggested at the time that van der Linde had influenced Lehnberg in order to get her to murder his wife but this was not proven and he was never charged.
Susanna van der Linde's body was discovered at about 1 p.m. by her daughter. Van der Linde attempted to telephone his wife a number of times that morning and eventually became concerned when there was no reply. He spoke to his daughter Zelda, who worked at Tygerberg Hospital, and asked her to go home during her lunch break to see if there was anything wrong. When she arrived home, the house was locked up, but through a window she caught a glimpse of her mother, who was lying on the floor in the living room.
The police immediately began an intensive murder investigation. Their chief suspect was a crippled Coloured man who had been seen in the area on at least two occasions prior to the murder. In fact, it was because of Choegoe that Mrs van der Linde insisted that her husband buy her a dye pistol. At first nobody considered that Lehnberg was involved, or that she could have hired an assassin.
For the next week, police efforts to establish Choegoe's identity and whereabouts proved fruitless. Then, on 13 November, the breakthrough occurred. At around 7.30 a.m. on the morning of 13 November, Lieutenant Roland Fourie of the Brixton Murder and Robbery Squad in Johannesburg went to see Lehnberg who was staying at her uncle's house in Bryanston, and asked her to accompany him to Brixton Police Station where he wished to ask her some questions. Lehnberg admitted on the way to the police station that van der Linde was her lover and that she had been expecting the police to contact her in connection with the death of his wife ever since she had learnt of the murder of Susanna van der Linde from her mother.
When asked if she had an association with a Coloured man named Marthinus she denied the allegation. Lieutenant Fourie also asked her if she had once requested a Mr Robert Newman to give her his pistol so that she could get rid of Mrs van der Linde. Lehnberg admitted that she had, but that the request had been made in fun. Although Lieutenant Fourie had no specific evidence to tie Lehnberg to the murder, it did strike him that she seemed unnaturally nervous at times during the interview.
While Lieutenant Fourie was on the telephone to Cape Town, another detective, Major van Aswegen, began asking Lehnberg questions. Suddenly, she blurted out that she took Choegoe to the house and waited for him, taking him home afterwards.
Lehnberg was arrested and formally charged with the murder of Mrs van der Linde. Later that day, she made a full statement in which she admitted that she had asked Marthinus Choegoe, a leg patient at the Red Cross Children's Hospital, if he would do away with Mrs van der Linde. In the statement she claimed that she had waited in the car while her accomplice had committed the crime. Choegoe was arrested the same day.
The trial of Marlene Lehnberg and Marthinus Charles Choegoe began at the Cape Town Supreme Court on 5 March 1975. The trial drew hundreds of spectators who fought for seats in the packed courtroom. After a hearing which lasted seven days and during which the State called more than 30 witnesses, the Judge, Justice Diemont, and his two assessors, Mr A.J. van Niekerk and Mr F. van Zyl Smith, deliberated overnight after which they returned verdicts of guilty for both accused. The court found no extenuating circumstances and Lehnberg and Choegoe were sentenced to death.
The third member of the tragic triangle, Christiaan van der Linde, died a lonely man in 1983. After the trial, he moved to Krugersdorp so that he could visit his wife's grave on her family's farm in the Magaliesberg mountains every day. He expressed remorse of ever having met Marlene Lehnberg.