Libya releases detained ICC staff members (AP) ZINTAN, Libya - Libya released on Monday four International Criminal Court staffers who had been held for nearly four weeks on allegations that they shared documents that could harm national security with Moammar Qaddafi's imprisoned son Seif al-Islam Qaddafi. As they were released, ICC President Sang-Hyun Song, a South Korean judge, apologized to the Libyan government and people for the incident and promised an investigation into the allegations. Song flew to Libya for the handover. "The ICC is grateful to the Libyan authorities for their agreement today to release the Court's staff members so that they can be reunited with their families," Song said as the four were released. A special flight arranged by the Italian government and carrying Song and the staffers landed at Rome's Ciampino airport late Monday. The staffers and Song took off for Rotterdam a few minutes later. The staffers did not speak to the media. "Well, I'm very happy to bring them all back to freedom," the court president told reporters. The Libyan government gave me their version of the investigation. We will do our own separately, so the results will be known after some weeks," Song added. U.N. demands release of detained International Criminal Court staff in Libya Seif al-Islam was the most senior member of the ousted Qaddafi regime to be captured in last year's civil war. Long viewed as a likely heir-apparent to his father, he faces charges by the ICC of crimes against humanity. He was captured by a militia in western Libya after his father was taken captive and then killed last October following more than 40 years as Libya's eccentric, authoritarian ruler. Seif al-Islam Qaddafi, son of embattled Libyan leader Muammar Qaddafi, embraces his brother Mohammad during the funeral of their brother Seif al-Arab Qaddafi at the Al-Hani cemetery in Tripoli, Libya, May 2, 2011. Credit: AFP/Getty Images Libya's new leadership accused Seif al-Islam of torturing and killing rebels, as well as other crimes. His trial has been at the heart of a dispute between the ICC and the Libyan government. Libyan authorities have challenged the ICC's right to try Seif al-Islam, saying the international court is a tribunal of last resort, intended to try suspects from countries that cannot or will not prosecute them. The court had expressed concern that Libya's judiciary is not yet ready to give Seif al-Islam a fair trial. The ICC judges ruled on June 1 that Libya doesn't have to hand over Seif al-Islam at least until a ruling on Tripoli's challenge. Richard Dicker, international justice program director at Human Rights Watch, said the release of the ICC employees was "overdue," and that if Libya had any concern over their conduct, it should have submitted a complaint to the ICC. "It is unacceptable that the ICC staff would be held for nearly a month when Libya had no right to do so," he said in an email to The Associated Press. Amnesty International echoed the same sentiment and urged the ICC to investigate the legality of the detention and the allegations made by the Libyan authorities. It also questioned Tripoli's readiness to offer Qaddafi's son a fair trial. "Not only has it denied them (the ICC staffers) their liberty and stopped them from performing their functions, but it has also undermined Seif al-Islam Qaddafi's right to an effective defense and delayed the ICC's decision on the Libyan authorities' recent application to bring him to trial in Libyan courts," said Amnesty International's Marek Marczynski. He urged the ICC to review the impact of the detention and take measures to ensure Qaddafi's defense team has time to prepare their case. The Libyan lawyer who represents Tripoli's interests at the ICC, Ahmed Al-Jehani, said the mission staffers were released because they have diplomatic immunity. Libyan authorities say they placed Australian defense attorney Melinda Taylor and her Lebanese translator under house arrest after they visited Seif al-Islam in prison in the western town of Zintan and allegedly shared documents that could harm the country's national security. Seif al-Islam was captured by Zintani rebels late last year and has been held there ever since. Al-Jehani said state prosecutors accused Taylor of having Seif al-Islam sign three blank pieces of paper, but they could not press charges because she has diplomatic immunity. Al-Jehani said Libyan authorities do not know why she wanted his signature. Libyan Deputy Foreign Minister Mohammed Aziz said the staffers, which also include a Russia national and a Spanish national, will leave to Tripoli and then Italy later in the day. Al-Jehani, who is also the Libyan prosecutor leading the case against Qaddafi's son, said they were in good health. He said the case has now been closed in Libya and the staffers will not return. "Definitely they are free and they will not be coming back to Libya," he said. Al-Jehani said the detention of the ICC staff has further complicated relations with Libya. "The relationship has become more difficult and more unstable," he said, adding that Libya would likely press ahead with its case against Seif al-Islam after the country's first nationwide elections this week to choose a parliament.Iran acknowledged that the measures were taking a toll, saying it has stockpiled goods and hard currency to help cushion the economy.