Duluth police have arrested four people in connection with the shooting death of a St. Paul police sergeant's 22-year-old son. A fifth suspect was already in custody.

Officers, with help from the Lake Superior Drug and Violent Crimes Task Force, arrested the four Friday as part of their investigation into William Andrew Grahek's death.

Grahek was shot at a residence in the 500 block of E. 11th Street on Feb. 14. He was taken to a hospital, where he died.

Police have turned their evidence over to the St. Louis County attorney's office for possible charges, saying they expect charges Tuesday. The Star Tribune generally does not name suspects before they are charged.

Three of those in custody, all men, are expected to face second-degree intentional homicide charges. The fourth, a woman, could be charged with aiding and abetting second-degree homicide, and the fifth, a man, with aiding an offender, police said.

Grahek, who was a student at the University of Minnesota Duluth, was a graduate of Centennial High School in Circle Pines. He was the son of St. Paul police Sgt. Jon Grahek.