A 41-year-old Swede with a long criminal record pleaded not guilty Friday to killing Prime Minister Olof Palme in a case that has frustrated this orderly nation for nearly three years.

Christer Pettersson was arraigned at Stockholm District Court, and a judge ordered him held for further questioning. Press reports hailed his arrest Wednesday as a breakthrough in the investigation.Palme, a four-term prime minister who championed leftist causes, human rights and disarmament, was killed Feb. 28, 1986 while walking home unguarded from a late movie in downtown Stockholm with his wife.

The assassination shocked Sweden, which prides itself on its orderliness, tolerance and lack of political violence.