Expert evidence is permitted in a criminal trial to provide you with scientific or medical information and the like which is within that witness's expertise but is likely to be outside your own experience and knowledge. I am sure you appreciate it is quite common for evidence of this type to be brought, but it is important that you see it in its proper perspective, which is that it is just part of the evidence as a whole which you have to assess on those individual aspects of the case with which each such witness dealt.
Just turning for a moment to two particular witnesses, Mr. Rideard and Mr. Baxter, who talked about the hammer and the lead piping, I just add one important note of guidance. Most of the experts, for example when it comes to mind the geologists probably gave evidence well beyond the experience of any of us, but Mr. Rideard told us about the effect of hammer on lead. He was shown impressions made by Mr. Baxter, and Mr. Baxter gave evidence about them. It is possible you might form some sort of visual views of your own about such common everyday items such as hammers. However, in the context of this case, with respect, you and I are not experts on this subject and it would be wrong for you to compare impressions taken by the witnesses with any speculation as to the type of marks which you think might be made by this hammer. It would be equally wrong for you to attempt to assimilate tests of your own in any area of expert evidence. It is not for you to go knocking around with the hammers when you get to your jury room, may I put it that way.