When British security authorities discovered that Osman Khan was the terrorist who stabbed a man and woman knife and stabbed another two at London Bridge, they should not have been surprised. The terrorist was known to the law enforcement authorities in the kingdom; He was jailed for eight years for attempting to blow up the exchange and intends to set up a terrorist training camp in Kashmir territory.

Despite these serious transgressions, he was released from prison with no guarantee he would not return, and was even invited to attend a conference on justice and rehabilitation after leaving prison on the north side of London Bridge, where he began his murderous assault.

Terrorists who return after being released from prison are a recognized phenomenon, and the State of Israel has been dealing with it for years. Many terrorists who were released in the Jibril deal and Gilad Shalit's release deal returned to terror and were responsible for the attacks engraved in the national consciousness.

Khan was not released in the deal like many of the terrorists who murdered and wounded Israelis, but even with us, under the radar and without much media noise, prisoners with blood on their hands are released from prison. What do you do with them afterwards? Is there some kind of oversight after they are released? These are questions that the Israeli public forgets to ask. We seem to settle for the terrorists' entry into the prison and forget that their desire to kill innocents as a means of furthering their goals, whether in Jerusalem or London, is not a passing thing, but an ideology with a regular subset, one that even the years in prison do not erase.

A similar principle applies to "former" terrorists. ISIS was defeated, and that's good news. The bad news is that thousands of his fighters and commanders, some Europeans, including some Israelis, are looking for a new home to further the vision of the Islamic Caliphate. These people may migrate en masse from Syria and Iraq and flood Europe's cities. There, they may join dormant or active terror cells, marking the blood for the third decade of the 20th century.

European countries, as well as Israel, must have a regular plan detailing exactly what to do with those people and how to ensure that they do not import the horrors and killings into their new homes.

Osman Khan wore an electronic bracelet when he was seized and liquidated by UK police yesterday. The movements of liberated terrorists can and should be monitored, whether they belong to al-Qaeda, ISIS or Hamas, but it cannot be expected that this will prevent the next attack. After all, terror is essentially designed to shake civilian complexes in order to sow as much fear as possible. What is needed is a plan that will not only remove the physical barrier to perpetrating an attack, but will primarily displace the murderous ideology that causes it.