Dozens of people gathered in Ghana's capital on Friday to pay tribute to an investigative journalist who was killed after helping to expose corruption in African football.Ahmed Hussein-Suale, part of a team that carried out an undercover investigation, was gunned down in the Madina suburb of Accra on January 16.The shooting was a rare assault on the press in Ghana, which prides itself as being one of the most stable democracies in an often turbulent region and a beacon of media freedom.Many of the lawmakers, diplomats, politicians and journalists who gathered for the memorial called for justice to prevail."Hussein-Suale's case must be resolved and the perpetrators brought to book," said Roland Affail Monney, president of the Ghana Journalists Association where the ceremony was held. "We call on the police to investigate this case thoroughly to ensure justice is served.".Police on Thursday said they had arrested six people over the shooting but they had been granted bail."My men will not rest until all those who perpetrated this heinous threat are exposed," police official Ampah Bennin said.Detectives say they have questioned Kwesi Nyantakyi, the former president of the Ghana Football Association (GFA) who was forced to step down because of the expose.Undercover journalist Anas Aremeyaw Anas, who led the investigation, was also quizzed, while a statement was taken from Kennedy Agyapong, a veteran lawmaker and businessman.Agyapong, a prominent figure in President Nana Akufo-Addo's ruling New Patriotic Party (NPP), published a photograph of Hussein-Suale on his private television channel.He also offered to pay anyone who attacked the journalist. The broadcast prompted Hussein-Suale to lodge a complaint with the police.The documentary into football corruption by Anas's Tiger Eye investigation team was aired by the BBC last June and exposed rampant match-fixing and bribe-taking.Nyantakyi resigned and was later banned for life by world governing body FIFA, while dozens of other football officials in Ghana and across Africa were sanctioned.Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.