Joe Karam argued in David and Goliath that David Bain could not have committed the murders because he wasn't in the house when the computer was turned on.  He based this argument on his calculations of the computer turn on time and of witness reports of David arriving home. He did not take into account, however, all the margins of error involved in both the calculated and reported times.

When assessing the computer turn on time and David's reported arrival at 65 Every Street by Denise Lahey, the following margins of error have to be considered:

• The setting of the time on Denise Lahey's car clock.  This she reported to be up to 5 minutes out, apparently 5 minutes fast, but who knows.
• Denise Lahey's memory recall of the time on the clock when she saw David.  She testified at least twice and on each occasion gave a different time. The final time given was 6.50, which if the clock was five minutes fast, changes to 6.45, but we need to give it several minutes' margin of error and +-5 minutes is probably fair
• The setting of the time of the computer.  This would have been set according to someone's watch or clock which carries a margin of error.
• The assessment of the computer turn on time done by the technicians when attempting to establish it.  In the PCA Report this is given as anytime between 6.39 and 6.49.

The margin of error of Denise Lahey's reported time overlaps that of the computer turn on time sufficiently for David Bain to have turned on the computer.