David testified to being the only one who knew where the trigger key was kept

By Kent Parker - Posted on 09 January 2013

Probability David: 
Probability Robin: 
Probability Incidental: 

It is possible that Robin knew where it was kept and was able to access it easily, but Robin already had it, since it was given to him by David the day before during the mid-winter swim and it was still in his possession but unused on the morning of the murders.  It is also possible that the rifle was unlocked.  When assessing this item it should be noted that the rifle belonged to David and he controlled its whereabouts.