How to collect Aconite, the rare substance needed for fast poison

[PZ]

In my first play through, I saw a fast-acting poison available at the Doctor's shop, but you need to complete a shop quest before you can purchase the substance.  Most of the items are easy to find, but one, aconite, is very difficult.  I've read reports that it can only be found by looting the bodies of the robbers, or by tackling Borgia messengers.

Yesterday as I was perusing the 'net, I stumbled upon instructions on how to find the elusive substance. The instructions sounded kind of goofy, so I was not too hopeful, but it turns out that it works splendidly.

Starting out at the Tiber hideout (Ezio's headquarters), enter the tunnels with the Thieves Guild as the destination.  As you emerge from the tunnels, turn to your right and look down the road, which forks to the right and left in a "Y" shape.  Wait for less than a minute and a Borgia messenger will appear running toward you from the left fork - tackle him to collect what he carries.  The messengers carry all kinds of things, so the chances of collecting aconite the first time is rather slim. 

If you are not successful the first time, enter the tunnels to return to the Tiber hideout, and then come back to the Thieves Guild - the messenger will spawn again so that you can repeat the process until you finally get the aconite.  It took me four tries this morning - less that 15 minutes - now all I need do is find some nutmeg, which is relatively plentiful.