Simplify the following text for a Grade 7 native English-speaking person.
Original: Dennis Lynn Rader ( born March 9 , 1945 ) is an American serial killer who murdered ten people in Sedgwick County ( in and around Wichita , Kansas ) , between 1974 and 1991 .
Simplified: Dennis Lynn Rader ( born March 9 , 1945 ) is an American serial killer . He murdered 10 people near Wichita , Kansas between 1974 and 1991 .