Half of the eight workers shot to death at an Indianapolis FedEx facility by a former employee before he killed himself belonged to the Sikh religious community, leading an advocacy group to urge a probe of possible racial or ethnic hatred as a factor.

Law enforcement officials said Friday they have yet to determine what motivated the gunman, 19-year-old Brandon Hole, who was white, to carry out Thursday night’s rampage, at a FedEx operations centre near Indianapolis International Airport...