Tripoli , Libya ( CNN ) -- The International Criminal Court demanded Saturday the immediate release of a lawyer and three other staff members who were detained while visiting the son of deposed Libyan dictator Moammar Gadhafi . Defense lawyer Melinda Taylor was detained in the city of Zintan after she was discovered carrying documents and letters Libyan authorities said jeopardizes Libyan national security , said Ahmed Gehani , a Libyan lawyer who serves as a liaison with the criminal court in The Hague , Netherlands . He said guards first confiscated a camera pen on Taylor and allowed her to go in to interview Saif al-Islam Gadhafi , who was captured in hiding last November . A later search by female guards found documents and letters written by former regime members , Gehani said . They included a letter from Mohammed Ismail , Saif Gadhafi 's former right-hand man . Taylor was also carrying three blank papers signed by Saif Gadhafi , Gehani said . Taylor is not in jail , but was placed under house arrest in Zintan , along with a translator . Gehani said Libyan authorities are looking into whether she was spying and communicating with the enemy . The two other court members from the registry office were free to go but chose to remain with Taylor and the translator . Gehani said a criminal court delegation is scheduled to arrive in Tripoli Sunday to try to resolve the situation . Judge Sang-Hyun Song , the president of the criminal court , said the staffers have immunity while traveling on an official court mission . `` We are very concerned about the safety of our staff in the absence of any contact with them , '' he said . Court spokesman Fadi El Abdallah said the court has had no contact with the four staff members . Nor has it received any official information from the Libyans as to why they were detained . `` We lost contact with them on Thursday , and since then we have had no opportunity to clarify the reasons for their detention , '' Abdallah said . `` When we got a hold of the Libyan authorities they only said that they would be released soon , but they did n't say the reason for why they had been detained , '' he said . Both the International Criminal Court and Libya 's new authorities want to put Saif Gadhafi on trial . The criminal court has demanded that Libya hand him over immediately to face accusations of crimes against humanity . Libya appealed the decision , saying that he should be tried at home . The criminal court issued an arrest warrant for Saif Gadhafi , who stands accused of having a role in the deaths of Libyans who protested his father 's 42 years of dictatorship . Taylor and lawyer Xavier-Jean Keita said in April that Saif Gadhafi has been mistreated and `` physically attacked '' since his capture . In a strongly worded statement , the lawyers described Gadhafi as being in a legal black hole , held in total isolation except for visits from officials . He also suffers dental pain because he has n't had treatment , and Libyan authorities have given him nothing to remedy the pain , the lawyers said . CNN 's Per Nyberg contributed to this report .
NEW : Libyans authorities investigating lawyer Melinda Taylor over documents . She and three other International criminal Court staffers were detained . They had gone to Libya , Zintan , to meet with Melinda Taylor son . Melinda Taylor stands accused of involvement in the deaths of protesters .