There was probably a time when the world was much smaller and more innocent where you could do the sort of infiltration an assassin needs. In Day of the Jackal, foreginers in the countries of Europe were a common sight and unremarkable. Security devices on ID that an amateur could not duplicate are relatively modern; also the ability to check ID using cell phones and computers.
Back in the day, fake passports were easy. DotJ used the old “find a old dead baby and use that name for a passport”, a trick very common and since 9/11 much more difficult. Of course, with government resources a lot of fake ID’s are easy.
You still have the problem of blending in. A white guy in Pakistan or China is a lot more remarkable than an Englishman in Paris, especially a quiet one. Surveillance for preparation is especially tricky when the target is easily spooked. So, you will need a variety of assassins in all sizes and colours. When one of the neighbours got friendly and asked OBL’s courier for his cell number,I’m sure he had someone ask around to see if this was a recent import or someone who had a long history in the neighbourhood.
One thing I wondered was why the team did not, for example, fly in a jeep or something and drive up to the house from out of town to minimize the warning (Terrain dd not allow it, I assume). If some guy half a mile away was complaining about the helicopter noise, OBL and his guys must have known what was coming. (Surprising they did not have panic rooms with hidden doors, tunnels to next door etc.)
As a side note, it’s impossible to keep something quiet when 20 or 50 people know, epecially if there’s a $50M reward. I’m sure the reason OBL hid so well was that only the people in the compound, and maybe 1 or 2 others, had any idea even what area of Pakistan he was hiding in.
Plus, if you recall Iran-Contra or Watergate or any other inquiries and especially trials of organized crime, “special ops” or hit men outside of the army seem more often than not to be flaming nutbars, not cool professionals. It’s not like you go and recruit these guys, and I assume “lone assassin” is a very different animal than “Navy SEAL”. (According to the news, typically SEALs are BA or MA university graduates, not some street-smart punk)