Police in Denver began registering residents' semiautomatic assault weapons under a new city ordinance, while opponents threatened to file a lawsuit challenging its constitutionality. Only one gun owner, the city's former chief district attorney, showed up during the first hour. The ordinance was introduced in the wake of growing gang activity in the city. Some semiautomatic owners were said to oppose registration because of fears that the City Council will eventually ban their weapons. Failure to register a weapon with a magazine of more than 20 rounds can bring fines of $100 to $999 and jail terms of 10 days to six months.