Marcel Steyn, 21, the youngest alleged member of the so-called "Krugersdorp Killers", dubbed "Electus per Deus" (Chosen by God), tearfully apologised on Monday during her testimony in the Gauteng High Court in Johannesburg, Netwerk24 reported.Steyn is the last of the three accused to testify in the case following the conclusion of the testimonies of Cecilia Steyn, 38, and Zak Valentine, 35, at the end of last year. The State has depicted Cecilia as the mastermind behind 11 murders and a number of fraud-related cases between 2012 and 2016. All three accused have pleaded not guilty.Marcel's brother, Le Roux Steyn, was also a part of the group, but he entered into a plea bargain with the State in May. He was sentenced to 35 years in prison for each of the seven counts of murder he was convicted of. Ten years of his sentence were suspended on condition that he testifies in the trial, News24 previously reported.Marcel's mother, former teacher Marinda Steyn, was sentenced to 11 life terms and 115 years imprisonment.'I am so sorry'Before the court adjourned on Monday, Marcel was reportedly asked if she wanted to say something to the families of the victims.Breaking down in tears, she said: "I am very sorry. I know the testimony and a confession will not bring them back. I also know it won't take away the pain. I realise you will have to live with that pain for the rest of your lives and I contributed to that. I am so sorry, I am so sorry," Steyn said.From the outset, many were surprised by Marcel's revelations about her involvement in many of the crimes.Krugersdorp News reported that, prior to Monday's proceedings, the testimony others had given insinuated that Marcel was not involved in any of the crimes.But as she started her testimony, Marcel said she no longer wanted to lie – she wanted to tell the truth, Netwerk24 reported.15 when first murder committedMarcel was 15 years old when the first murders were committed in 2012, according to Netwerk24. She was living with Cecilia, who was taking care of her, at the time.Cecilia then tasked her with sending death threats from several cellphone numbers. Marcel felt proud to have been given this responsibility. She initially liked Cecilia and felt she had something in common with her after Cecilia told her they had the "same demons", she testified.READ: 'Krugersdorp killer' Marinda Steyn describes her first murder as 'exciting' and an 'adrenaline rush'Marcel testified she now realised Cecilia was not the person she pretended to be and that she no longer wanted to lie. She said she was scared."I don't know how Cecilia is going to react. I don't know who she will use to get to me," she said. Judge Ellem Jacob Francis granted a protection order.Marcel then testified that Electus per Deus was centred on Cecilia and that the group would do anything she wanted because she had been "elected by God". Marcel said she could not find anything in the Bible to justify the murders committed "in the name of God", but had no one to talk to.Marcel was reportedly not present at the murders of Natacha Burger and Joy Boonzaier, but she was tasked with cleaning blood from the knife. She accompanied her mother to the murder of the elderly pastor Reg Bendixen. She stood 10 metres away and witnessed the murder, she testified.'I was looking at my mother stabbing her'Marcel also broke down in court while describing how her mother, Marinda, used a hammer to beat travel agent Mikeila Valentine on the head, Times Live reported.Mikeila Valentine was Zak Valentine's wife and Cecilia reportedly ordered her murder because she was considered a "loose string".Marcel reportedly said Cecilia had arranged with Zak to give Mikeila medication the night before. She said when they arrived at the house, they found Mikeila sleeping in bed.ALSO READ: Cecilia Steyn denies being a satanistShe said she watched as her mother went in and used a hammer to hit Mikeila on the head."My mother put the hammer down and started stabbing her. I stood there and I just froze. I just kept on thinking and felt that this was Mikeila," Steyn reportedly said while wiping her tears."I stood there and I was looking at my mother stabbing her," she reportedly testified.Marcel's brother Le Roux earlier testified that she was a "diligent student" who had a promising future, News24 reported."My sister was a top achiever. She matriculated with six distinctions in her matric year (2015)," Le Roux Steyn told the court.The trial continues.