What do we know about the terrorist behind the Sydney siege?

(CNN) - A gunman, ISIS sympathizer and self-proclaimed Islamic cleric named Man Haron Monis took more than a dozen people hostage at a popular Sydney cafe for more than 16 hours today.

Australian special forces, along with heavily armed police, stormed the cafe at 2 am local time, killing the gunman. At least two hostages were killed during the rescue attempt and four others wounded.

So just what do Australian and American officials know about the hostage taker?

CNN correspondent Atika Shubert dug into the killer's background and joined "The Lead" live from London to discuss.