First there is no central office which is responsable from A to Z for everything concerning the transfer of prisoners. The risk analysis of each prisoner who needs to be transferred is done by the different departments with different objectives.
Second the people who have to safeguard the security of those transfers have NO GUNS. You read it right. THe persons who have to guard sometimes very dangerous criminals (with limited risks because they have been behaving well lately) have NO arms. They also don't have the powers of the police, they are only administrative workers. If the risk of evasion is too high or there are other risks the police is asked to do the transfer.
Third the service responsable for the transfer of the prisonsers has not enough manpower, especially during holidays, after standard working hours or when they have too many transfers at the same time.
Fourth the Justice Palace in Brussels where those court sessions are being held is in fact a protected monument. It is a really impressive building (built to impress the population living around it) but it is not a building that could be used for court sessions with dangerous criminals. Even placing cameras can take months because each change has to agreed by a kind of architectural protection commission. Maybe the court sessions for dangerous criminals should be held in the prisons themselves. We are planning to build new ones anyhow.
Fifth as several politicians are all responsable for part of the problem, the blame game has begun.