Casino executives in Macau have boosted their personal security after one of the city's most colourful gaming bosses was maimed in a vicious gang attack and three casino customers were murdered in the space of two weeks. The violence has led to concerns of a return to the dark days of the late 1990s as the city's gambling industry faces its first real cash squeeze since liberalisation 10 years ago. Ng Man-sun, the Mong Kok wet market trader turned casino boss, who is widely known by the nickname 'Gai See Wai'' or 'Street Market Wai'', remains in a stable condition in Macau's Hospital Conde de Sao Januario under the protection of bodyguards after a brutal attack late last month by a gang of six men as he dined with a woman friend in a restaurant in the New Century Hotel on Taipa. Ng is a major investor in the Greek Mythology Casino, which is housed in the hotel and operates under Stanley Ho Hung-sun's SJM concession. Gaming insiders said that the attackers deliberately severed the tendons on Ng's arms and legs to cause permanent damage, and security experts say the beating bore all the hallmarks of a triad attack. It was followed by the killing of a mainland woman several days ago in a residential area minutes away from the Venetian Macau casino and came just days after two mainland men were murdered at the five-star Grand Lapa Hotel, formerly the Mandarin Oriental. The police are not connecting the attacks but the outbreak of violence has evoked memories of the late 1990s, when the then Portuguese-run enclave was rocked by assassinations, car bombings and gangland attacks as rival gangs battled for the control of the city's highly lucrative VIP gambling rooms. Authorities in both Macau and the mainland are also becoming increasingly jittery ahead of the release from prison later this year of the notorious 14K triad society boss 'Broken Tooth' Wan Kuok-koi, who wreaked havoc in the late 1990s. His associates are understood to still work in the junket business, through whose often opaque operations the high-rollers who account for the bulk of Macau's casino revenue, and hence its tax revenues, are brought to the city. The pace of growth in casino revenues has slowed over the past three months. This has forced junket operators to adopt more aggressive debt-collection tactics. Last week gambling shares tumbled and Fitch Ratings slashed its forecast on the city's gaming revenue growth. Security sources have also told the Sunday Morning Post that there has been a noticeable drop in the number of mainland visitors to Macau in recent weeks. It is not clear if this is the result of an official move to cut travellers or because of squeezed liquidity on the mainland. An insider with more than 20 years' experience in the city's casinos said: 'The smaller junket operators are finding it increasingly difficult to collect debt and in turn the bigger junket businesses are struggling to pay up to the casino operators. Everyone is on edge. 'Top executives - even if they are far removed from the shady end of the junket market - are scared and are taking measures to be on the safe side. Throw in the impending release of 'Broken Tooth' and you have a perfect storm. No one is saying it's back to the 1990s but people are worried.' A number of possible motives for the attack on Ng, who successfully sued a now defunct Hong Kong magazine for libel 22 years ago after it claimed he was a triad leader, ran illegal gambling dens and was involved in organising a murder, have been put forward. One is that it involves a personal dispute between Ng and his long-time girlfriend, another that it is connected to a dispute related to Ng's shareholding in the Hong Kong-listed Amax Holdings, and a third that a debt of some sort was involved. Last week Ng paid for an advert in a Macau newspaper offering a HK$10 million reward for information leading to the arrest and prosecution of the mastermind behind the attack. Macau's Judiciary Police are still investigating all four crimes.