Deliberate mistake: A father, daughter (both construction\demolition experts) and the boyfriend try to frame the husband for attempted murder by planting a pipe bomb in her (wife\daughter\girlfriend's) car. The bomb is a stick of dynamite inside a pipe with 2 endcaps on it. A pipe is used to hold a improvised munition together: i.e., homemade explosives, or something like Anfo. The pipe provides the casing for the explosive material. Or, it is used to keep the shrapnel fragments around the explosives (like nails or pellets around a stick of dynamite). For dynamite, you simply drill a hole (in rock, in concrete, in whatever.) and drop the stick in. It needs no extra casing. The family would have known that. But the CSI crew needed some evidence to analyze and the blasting cap + detonator circuit would have given them nothing to study. The endcap with the hole drilled for the blasting cap was the case solver.