Protesters marched through downtown Atlanta Tuesday to voice their opposition to construction of a police training center outside of the city. More than 20 people were arrested at the site on Sunday and an environmental activist was shot to death by police during a raid at a protest camp in January. There was a heavy police presence as marchers walked along city streets. More than 20 people from around the country face domestic terrorism charges after dozens in black masks attacked the site of a police training center under construction in a wooded area outside Atlanta, the flashpoint of conflict between authorities and left-leaning protesters.