WASHINGTON - June 10, 2010 - Nearly 400 people were convicted of driving while intoxicated in the District since fall 2008 based on inaccurate results from breath test machines, and half of them went to jail, city officials said Wednesday.

D.C. Attorney General Peter Nickles said the machines were improperly adjusted by city police. The jailed defendants generally served at least five days, he said.

Nickles's office has begun notifying the drivers, a move that immediately triggered at least one lawsuit against the District and could lead to requests for expungements, new trials and even deeper skepticism about the integrity of testing. Challenging test results is at the heart of drunk driving cases, and this revelation will only strengthen those challenges, defense attorneys said.

The District's badly calibrated equipment would show a driver's blood-alcohol content to be about 20% higher than it actually was, Nickles said. All 10 of the breath test machines used by District police were wrong, he said. The problem occurred when the officer in charge of maintaining the machines improperly set the baseline alcohol concentration levels, Nickles said.