Your hypothesis piece of argument may seen factually as perfect
if indepth thoughts are not given. Also, in the argument for the
abolishing of the death sentence based on this scenerio alone,
would not carry much weightage in my humble opinion.
The presumption of law has always been this way whether by
reduction the mandatory death sentence to life imprisonment or not.
It is only the latter that when a person who has been later found
to be wrongfully imprisoned, then justice can be rightly returned.
In this case, there is a delayed in justice. One may argue that
sometime evidences only surface out a few years later after the
crime had been committed but this is more applicable to murder
cases than any clear cut drug trafficking case that we are debating
on.
Let me analyse your given scenerio from two sides of view, namely
the defendant and the drugs ring.
Defendent
The following can be vital clues to prove the motive of whether the
defendent did committed drugs trafficking.
1. Purpose of visiting the country named. If so, any
(i) Eye-witness(es)
(ii) Alibi
2. Particulars of defendent
(i) Social standing
(ii) Financial status
(iii) Family values
Drugs Ring
1. Is it wise to implant millions dollars worth of drugs on the
surface of an unknown vehicle since the interior is
out-of-bound.
2. Where should the drugs be planted at given the limited of
storage space on the exterior of a car.
3. Should the planting take place in broadday light or
night-time?
4. Are the drugs readily available anytime for the planting?
5. How to confirm whether the planted car is returning back home
and not going elsewhere?
6. Who is suppose to mann the car after it had been planted?
7. How many cars for tailing are needed to be efficiently carried
out?
8. What are the chances of getting busted?
Hence, is it wise for the drug rings to gamble with their drugs
which are worth millions dollars as stake with so many unknown
factors at hand.
The argument I have given is only based on legal principles and the
psychological prospective of the drugs ring for your scenerio. It
does not neccessarily support or denial the abolishing of death
sentence where in my opinion, political and social impacts play a
more crucial role. 
