Authorities arrest several people who allegedly planned to detonate homemade bombs during Bahrain's national celebrations in December 2008. In April 2009, the King pardoned more than 170 prisoners charged with endangering national security, including 35 Shias being tried on charges of trying to overthrow the state. However, in September 2010, in the run up to the elections, 20 Shia opposition leaders were arrested and accused of plotting to overthrow monarchy by promoting violent protests and sabotage. In the October parliamentary elections, the main Shia opposition group, Al Wefaq, could make only slender gains.