There was an intelligence informant who was a former Fatah member, code-named "Grotius" who was said to be familiar with the base in Karameh and its surroundings. Grotius is said to have arrived in Jordan as a member of the 421st Commando Battalion of the Palestine Liberation Army, on the eve of the Six-Day War. After deserting his battalion, he trained in Syria at the Hama camp and later slipped into the West Bank. Israel assumed that the Jordanians would ignore the invasion, however, the Israelis were met with heavy resistance from them.