The Hamas man assassinated was an enemy of the state and one of the duties of ALL intelligence services is to deal with threats to the state and on some cases that involves assassinations. As for the passports all the major intelligence agencies forge passports and use them to carry out operations abroad. I am sure there are plenty of Mossad agents who regularly travel in and out of foreign countries including friendly states like the US & UK and nobody ever picks up on it. Israel has spies in friendly states following individuals who are considered possible threats so they are just kept an eye on by agents who came into the country with false visas and false passports. Thats how the system works.
Report: Car bomb kills 10 in Syrian port city (AP)
from the article: Germany, France also request Israeli answers on Dubai fake passports