Review of The Ghost Position

I like the Vera series. But I wish this episode had been clearer on who the killer actually was. It's suggested, but not explicitly enough revealed. ~~~~~~ WARNING ~~~~~~~~ !!!! SPOILER ALERT BELOW !!!! !!!! SPOILER ALERT BELOW !!!! !!!! SPOILER ALERT BELOW !!!! Lena has to be the killer. But how did she get the materials together (and the know-how) to actually make the bombs? Doug died just testing one out. And he seemed to be a lot more competent than his fiance.