ST. LOUIS (AP) — Many Americans are convinced there was no justification for a suburban St. Louis police officer to kill 18-year-old Michael Brown, because Brown was unarmed.

Others are certain the shooting last month in Ferguson was justifiable because they believe Brown threatened the officer.

But according to a CBS News/New York Times poll, 64 percent of respondents said they didn't know enough to decide. Only about half said they'd paid "a lot" of attention to the case.

The national furor over the shooting is being fueled by those with strong opinions who are still marching or loudly supporting their side.

Psychologists say such strong opinions are often influenced by "confirmation bias." Research shows people search for evidence to support their preexisting viewpoints and interpret it in a way that reinforces their beliefs.