First as a journalist and later as executive director of CAMFAIDS, a Yaounde-based human rights organization, Lembembe documented violence, blackmail and arrests targeting members of Cameroon's gay community. Just two weeks before his death, he warned in a statement about the threat posed by "anti-gay thugs."
Though the precise motive for the killing is unclear, his friends have said Lembembe had no enemies and fear he was attacked because of his activism.
Lembembe is the most high-profile African gay rights activist to be killed since 2011, a year that saw the deaths of Uganda's David Kato and South African lesbian activist Noxolo Nogwaza.
Cameroon punishes gay sex by up to five years in prison, and Human Rights Watch says the country pursues more anti-gay prosecutions than any other in sub-Saharan Africa.
Tchiroma said Friday that the case is being investigated, but rights groups say previous investigations of anti-gay violence have not been thorough.
"I don't trust the justice system, especially when the issue has to do with homosexuality," said Alice Nkom, one of the few lawyers in Cameroon willing to defend suspects charged under the country's anti-gay law. She said those who defend the rights of sexual minorities in Cameroon have long complained of threats and attacks with little response from the government. "It's a scandal for him to invite journalists and then to warn the civil society and foreign media to stop talking about it," she said.