The gray, concrete building looms over the street in central Beijing, CNN report.Completely unmarked aside from a street number, its entrance is buttressed by barriers and fencing. Inside lies an organization that strikes terror into the hearts of some of China's most powerful people, and oversees a sprawling network of secret prisons where experts say torture and abuse are common. The Central Commission for Discipline Inspection (CCDI) is the body tasked with investigating all 88 million members of the Chinese Communist Party for corruption. Witch hunt? Cracking down on corruption has been a key goal of Chinese President Xi Jinping since he came to power in 2012, and his tenure has seen the downfall of several of China's highest-ranking politicians, including former security tsar Zhou Yongkang and former top People's Liberation Army general Guo Boxiong. Xi has called for the Party's investigators to tackle both "tigers and flies," high-ranking officials and ordinary cadres. Almost 300,000 people were charged with graft offenses last year, according to CCDI deputy secretary Wu Yuliang. However, doubt has been raised over both the effectiveness of Xi's push, and whether there are other motivations behind it. "That's the big question about the campaign: is it an anti-corruption effort or a political witch hunt?" said Andrew Wedeman, head of Georgia State University's China Studies Initiative. "It's part of both." The CCDI did not respond to a written request for comment.