For three years we’ve been following the saga of 81 Spooner Road, the Brookline property at the center of a contentious zoning dispute and, more recently, an arson investigation.  See our original post here, and our follow-ups here, here and here.  Now, a trio of Northeastern University journalism students under the supervision of their professor – former Boston Globe Spotlight Team editor Walter V. Robinson – has taken a closer look at the arson case.  Their conclusion: while there’s some compelling evidence against the the suspect, his motive remains a mystery.  The students’ report, published in yesterday’s Globe (including a dramatic photo of the home’s charred shell), is here.