"Often in suicide cases the motive is never determined," Gray said in a statement. "In this instance, our investigation did not uncover any articulation by Bart as to why he took this particular action."
Palosz, 15, took his own life with a shotgun after the first day of the school year on Aug. 27. The gun was family-owned, registered and stored in a gun locker.
A collection of dark posts to a Google+ account attributed to Palosz revealed his mental state and suggested he may have been bullied for years.
The police opened the criminal investigation in early September.
Also in the statement, Gray called the suicide a "serious public health issue" and called on the general public, public officials and health and human service professionals to "work together" to reduce the chance of these incidents.
Gray also added that no further information would be released at this time in respect to Palosz's family.
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