Assume

The group of professionals had planned the hit for three months, every angle covered, they assumed.

The group of friends had 24 hours to get the money together, and an inside man, so it would be easy, they assumed.

The group all had their own enemies, who had come together to deal with them all quickly, suddenly, and thus would get away clean, they assumed.

The boss who had the friends by the balls wanted to ensure they were screwed, if not they might succeed, he assumed.

The sole survivor has all the money and lives under an assumed identity.