Johannesburg – Police were merely exercising their right when they arrested the Thulsie twins, the Johannesburg Magistrate's Court heard on Thursday.Prosecutor Chris MacAdam told Magistrate Pieter du Plessis that the three officers who arrested Brandon-Lee and Tony-Lee Thulsie did so based on the suspicion that they had committed a serious offence.Late on Thursday afternoon, Colonel Andre Neethling, a provincial investigator of crimes against the state, took the stand to testify against the 23-year-old twins.They were in court in an attempt to have their arrests declared unlawful.Neethling said he went to the house of Tony-Lee, where he met the investigating officer, Warrant Officer Wynand Olivier. Olivier told him that a witness, Renaldo Smith, acknowledged that he and the brothers were part of a group who wanted to leave South Africa to join terror group, the Islamic State (ISIS).The twins were allegedly plotting attacks on a US embassy and Jewish cultural sites in South Africa. They were arrested during raids in Newclare and Azaadville on Saturday, July 9. They face three counts of contravening the Protection of Constitutional Democracy Against Terrorist and Related Activities Act.On Monday, the court heard that Tony-Lee, using the alias Simba, allegedly communicated via social media with an Isis member planning an attack in South Africa. Neethling told the court on Thursday that he believed this was valuable information and enough to execute an arrest without a warrant.According to him, the officers decided to give Smith, who turned State witness, a warning.Earlier on Thursday, Olivier told the court that no explosives were found at any of the houses searched.The matter was postponed to Friday, where final arguments would be represented.