Last week’s near-fatal attack by unknown assailants on Kevin Lau, former chief editor of the newspaper Ming Pao, inspired thousands of media professionals and ordinary citizens to take to the streets of Hong Kong and demand the truth: who attacked Mr. Lau and why? It was more than an aggression on a single person; it represented a direct attack on Hong Kong’s press freedom.

Many Hong Kongers suspect Mr. Lau was ousted from Ming Pao in favor of an editor more willing to kowtow to Beijing. While the reasons behind the attack on Mr. Lau are unknown, media outlets around the world have taken an interest in the story questioning if there is any connection between his ouster and the brutal assault.

Chief Executive Leung Chun-ying must prove that Hong Kong remains one of the freest reporting environments in Asia and that journalists can work safely under his watch. Until the case of Mr. Lau is solved, he must ensure that the investigation is a top priority for police and journalists do not feel threatened when working in Hong Kong.

Rumors of China’s meddling in Hong Kong’s media are not new. Mainland companies and big international banks are known to have removed advertising from newspapers critical of the Chinese government. Hong Kong journalists have spoken of pressures they have received not to disclose certain stories, and a poll conducted last year by the University of Hong Kong found that more than half of the population thought the local media exercised self-censorship.

Ming Pao is a highly respected Chinese-language daily newspaper, known for investigative journalism and its critical reporting on China. When Mr. Lau was suddenly removed from his position as chief editor last month, the move caused an outcry in the industry and over 90 percent of Mr. Lau’s staff filed a petition demanding an explanation for the action. His replacement is a Malaysian Chinese editor considered to be pro-Beijing.

The attack on Mr. Lau was not the first aggression on a member of the Hong Kong media. Last year a warning message was sent to Jimmy Lai, publisher of the popular anti-Beijing newspaper Apple Daily. A car rammed into the front gate of his home and an axe and machete were placed in the driveway.

“There is a concern that something is going on,” says Doreen Weisenhaus, Director of Media Law Project & Associate Professor at the University of Hong Kong. Hong Kong people want the government to take a stand and investigate these cases, she said.

How the local government, and specifically the Chief Executive, handle this situation will speak volumes to critics who accuse Mr. Leung of being under Beijing’s influence. In the aftermath of the attack, he issued a statement saying he was “concerned and outraged about the attack,” and visited Mr. Lau in hospital. Now he must show he is serious about uncovering who is responsible for this attack and answer the questions the public is demanding answers to.