At 9:45 am local time on Monday (5:45 pm ET Sunday), a gunman entered the Lindt Chocolat Cafe in Sydney, Australia, taking an unknown number of staff and customers hostage. The unknown gunman was not shy about expressing his motives for the world to see, as he sent hostages to the front window to hold up an Islamic flag for news cameras to see.

Zain Ali, the head of the Islamic Studies Research Unit at the University of Auckland, said it was difficult to read the message because media images showed only the lower part of the flag. But he believed it was the Shahada, or declaration of faith, largely because a black flag with white writing in a contemporary context often contains that message. He said he could make out the word “Muhammad.”

Ali said the Shahada translates as “There is no deity of worship except God (Allah), and Muhammad is the messenger of God.” It is considered the first pillar of Islam’s five pillars of faith, and has been used by groups like al-Qaida and Islamic State but wasn’t invented by them, Ali said.