I'm naturaly suspicious of anything published in the Sunday Times, but if there really was a hit squad of 7 people with European passports, that does sound like Mossad. I can't imagine any Hamas faction or arms criminals going to such elaborate lengths. They'd just have walked in and killed him if they wanted to.
Austrian police say they expect 10,000 migrants to arrive from Hungary (DPA)
from the article: Dubai not ruling out Mossad hand in murder of Hamas official