ST. PAUL, Minn. (AP) - William Finney may be retired as St. Paul's police chief, but he's still helping fight crime.

Finney witnessed a stabbing last week on a light-rail platform in St. Paul. He followed the assailant while calling 911 and providing updates to police about his location.

Officers arrested a 17-year-old boy in the daytime stabbing, which happened Thursday. The 25-year-old victim suffered injuries that are not considered life-threatening.

Finney was a St. Paul police officer for nearly 34 years, spending the last dozen years as chief until retiring in 2004. He says he figured it was his job to act as "a good citizen and witness" and make sure no one else was hurt.

The 66-year-old is currently a member of the St. Paul City Council.