Didi, which completed a record 7.4 billion rides for 450 million users last year, suspended on Monday its carpool-like hitch service, which allows Didi-registered private car owners to give a lift to passengers travelling the same way.

Police in Leqing city, in China’s eastern Zhejiang province, said on Saturday they found the body of a 20-year-old female surnamed Zhao, and arrested a Didi driver who confessed to her rape and murder. The victim had sent a message to her friend a day earlier asking for help before she went missing.

That incident has prompted many people in China to download free smartphone apps to directly communicate with police. An app called Gong’an 110, which translates to Police 110 in English, ranked on top of a list of free apps downloaded from Apple’s online App Store in China on Monday.

Developed by Hebei Canglin Shishang Technology, Gong’an 110 allows users to directly make video calls and send text messages to police officers. Its video call function, however, is not available in Beijing, the nation’s capital.

Meanwhile, police have detained two men accused by Chinese social media users of making offensive remarks about the 20-year-old passenger who was killed last week, according to a Reuters report on Tuesday.

Police in the southern city of Shenzhen said they arrested a 22-year-old man who posted comments in a chat group on Tencent’s messaging service QQ. The group has over 1,000 members and calls itself the “Shenzhen Didi Exchange Group”.

The man’s comments “incited the righteous indignation of netizens and has caused a seriously adverse social impact,” Shenzhen police said in a statement on Monday.

A 29-year-old man was arrested separately in the central city of Wuhan after he made comments in a QQ group named the “Wuhan Didi Official Group”, Wuhan police said on their official Twitter-like Weibo account on Monday.

Under China’s internet rules, users who spread rumors or make defamatory comments can be arrested or even sent to jail.

Another popular free app being downloaded from the App Store is Beijing 110, developed under a commissioned project by the Beijing police. It can automatically share a user’s location with the police, as well as provide information on the direct line and address of the nearest police station a user can reach.

“I hope those who passed away using the Didi service could have downloaded [Gong’an 110] to protect themselves,” an anonymous user wrote in a review on Apple’s App Store on Sunday.

While the review section was mostly dominated with complaints about registration failure and other bug reports, another anonymous user urged people to be vigilant about safety. “Now is time to call police via live streaming … Everyone has responsibility to guard public security,” the user wrote.

An investor listed by Canglin Shishang Technology, based in northern Hebei province’s capital of Shijiazhuang, did not immediately respond to calls.

The latest incident has put the country’s fast-expanding ride-hailing sector under a cloud, as Didi pursues an initial public offering next year and seeks further investments in new businesses, such as its automotive solutions unit.

Didi counts hi-tech giants Apple, Alibaba Group Holding and Tencent Holdings among its biggest shareholders. Didi has a valuation of US$56 billion, based on its latest venture capital funding round last year. Alibaba is the parent company of the South China Morning Post.

On Monday, Alibaba’s AutoNavi announced the halt of ride-pooling bookings on its platform due to “security concerns”. Launched in March, the service was only available in Chengdu, the capital of southwestern China’s Sichuan province, and in Wuhan, capital of the central province of Hubei.

Public anger about the Didi case and the safety of ride-hailing ran high on Chinese social media over the weekend. It was the top trending topic on several news and microblog websites, with posts relating to the case having been read or reposted nearly 1 billion times on Chinese microblogging service Weibo.

Amid the public outcry, People’s Daily, the mouthpiece of Chinese Communist Party, criticised Didi on Weibo for being “impertinent” in failing to prevent the latest killing committed by one its registered drivers.

“No matter how timely the apology is, it can only look cheap without capability for correction,” People’s Daily said.

On Sunday, China’s police and transport ministry said in a statement that Didi had “unshirkable responsibility” for what happened to the passenger based on the investigation. It asked Didi to conduct a revamp of its hitch-riding service.

In May, another woman, aged 21, was raped and killed in Zhengzhou, in central China, allegedly by an unregistered Didi driver whose body was later found in a river.

Didi did not immediately respond to inquiries.

The company’s ride-hitching service, which was introduced three years ago, became a popular option for people who were unable to get a train ticket or afford more expensive air fares during China’s Lunar New Year. About half of the trips were between 30 and 100 kilometres, or one to four hours drive, according to Didi in February.

Didi remains the country’s largest ride-hailing platform with a penetration rate of 15 per cent as of August 20, according to third-party statistics provider Jiguang. It was followed by DiDa Chuxing and Ucar.

Still, a ride-hailing rival made sure the public knew what it was doing to ensure the safety of its passengers. Ucar posted on its public account on social-media platform WeChat on Monday an advertisement highlighting that the company owns its car fleet and that only one in eight drivers pass its qualifications, which ensure a minimum of three years driving experience.