COLUMBIA HEIGHTS\. (AP) - Authorities are investigating the killing of an adviser to students at a St. Paul charter high school.

Thirty-one-year-old Philip Charles Borer Nelson, of St. Louis Park, died early Thursday at an apartment in Columbia Heights. Nelson had worked for the past three years as an adviser mentoring students at the High School for the Recording Arts, where he was a 2005 graduate. He also had dreams of becoming a hip-hop producer.

Nelson's mother, Bridget Borer, tells the Star Tribune her son had gone to his ex-girlfriend's apartment ``to take care of a few things,'' but was gunned down, leaving his four children, ages 3 to 13, without a father.

The Anoka County sheriff's office was searching for a 41-year-old Brooklyn Park man who's described as a recent acquaintance of Nelson.