Ghanaian police on Thursday opened an investigation after an undercover journalist who helped expose corruption in African football was shot dead."Our men are on the ground currently gathering information", said the director of the criminal investigations department, Maame Yaa Tiwaa Addo-Dankwa"Everyone connected to this murder will be invited for questioning," he told AFP.Ahmed Husein was part of a team led by award-winning journalist Anas Aremeyaw Anas, whose probe led to the resignation of the head of the Ghana Football Association.Dozens of football referees and officials in several countries were also banned, including Nigerian national team coach Salisu Yusuf, for receiving cash from undercover journalists posing as agents.Husein was shot in the neck and the chest by unknown gunmen on his way home on Wednesday night in the capital Accra, police said.Confirming the incident, Anas tweeted: "Sad news, but we shall not be silenced. Rest in peace, Ahmed."Husein had previously made a complaint to police after a Ghanaian lawmaker, Kennedy Agyapong, showed his photograph on a private television channel.He promised payment for supporters who took retribution against Husein."That boy that's very dangerous, he lives here in Madina. If he comes here, beat him," he said, pointing to Husein's image.In the undercover investigation into football corruption, Agyapong's name was mentioned by implicated sporting officials.Husein's lawyer, Kissi Agyabeng, said the member of parliament had questions to answer."He invited the world to beat him up and said he will pay for it and now he has been killed," he said."How can you put pictures of someone out there and splash it on national TV and ask people to go after his life for a reward? In law this is abetment of crime." Press freedom The Committee for the Protection of Journalists called for an immediate investigation and for Ghanaian authorities to "ensure that threats against the press are taken seriously".Ghana ranked 23rd out of 180 countries in the Reporters Without Borders 2018 World Press Freedom Index - an improvement of three places on the previous year.RSF has previously condemned threats against Anas himself after he revealed "threatening calls, intimidatory messages and suspicious vehicles near his home".The reporter, whose other exposes have lifted the lid on graft in the judicial system, is distinctive for wearing hats and face-coverings to conceal his identity.He has also faced threats from Agyapong, who belongs to President Nana Akufo-Addo's ruling New Patriotic Party.Ghana's national media regulator condemned the killing."It will be in the national interest to arrest the perpetrators of this crime," the commission's chairperson Yaw Boadu Ayeboafo said in a statement.Ghanaian journalists condemned the killing of the 34-year-old reporter, who played a key role in last year's investigation.Football's world governing body FIFA last October banned former Ghana FA boss Kwesi Nyantakyi for life and fined him nearly $500 000 after he was seen on camera accepting bribes.Nyantakyi was accused of requesting $11m to secure government contracts.Eight referees and assistant referees were banned for life while 53 officials were subject to 10-year bans. Fourteen officials were exonerated.The revelations rocked Ghana, a country where football is the national sport and which prides itself as a stable democracy in an often turbulent region.Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.