A bus carrying Palestinian teenagers released from Israeli prisons arrived in the center of the West Bank city of Ramallah on Sunday afternoon, CNN reports.

Earlier, the Israel Prison Service confirmed that it had released 39 prisoners from a total of seven Israeli prisons, six in Israel and one in the occupied West Bank, in exchange for the release of 17 hostages from Hamas.

The current released prisoners are boys aged 18 and under, two are 15 and the youngest released is 14.

Some were held in jail without knowing the charge. Sixteen of those released were serving sentences, mostly for attacks on Israelis, according to information from the Israel Prison Service and the Palestinian Prisoners’ Association, a non-governmental organization that defends prisoners’ rights.

The remaining 23 who were released were under administrative detention, a widely criticized practice in which a detainee does not know what charge he is being held on while his case is not subject to any legal process.