ARUSHA, Tanzania — One of the most wanted suspects in Rwanda's 1994 genocide pleaded not guilty today to crimes against humanity at a U.N. tribunal trying the alleged masterminds of the slaughter.

The International Criminal Tribunal for Rwanda has charged Gregoire Ndahimana with being responsible for the deaths of about 2,000 Tutsis, most of whom died when bulldozers knocked down the church where they had sought refuge in the western Rwandan town of Kibuye.

Ndahimana, a former mayor, had been on the run for 15 years before he was captured in August in Congo. He had a $5 million bounty on his head but no one has claimed the reward. The tribunal later will set a date for Ndahimana's trial.

Twelve other top suspects have similar bounties on their heads for their alleged roles in the 1994 genocide. More than half a million members of the Tutsi ethnic minority and moderates from the Hutu majority were slaughtered during the 100-day genocide.

Many former Hutu militia leaders fled to Congo, which neighbors Rwanda, after Tutsi rebels fought their way to power.

The U.N. Security Council set up the International Criminal Tribunal for Rwanda in November 1994. It has so far convicted 36 people and acquitted six.

Judges are currently presiding over nine trials. Three suspects are still waiting for their trials to start. The Security Council has given the tribunal until December 2010 to complete all trials.