In Syria, we often hear about opponents of the Assad regime who have been behind bars since the beginning of the country's civil war. But another group of detainees remain surrounded in secrecy. There are more than 600 Lebanese citizens still in detention in Syria, after being imprisoned by Damascus during neighbouring Lebanon's civil war. In some cases, their families are still waiting for news after more than twenty years. Our correspondents Zeina Antonios and Leila Molana-Allen report.