Kenya's recently resigned anti-corruption czar could be in danger, a colleague has told the BBC.
Githongo has spent years fighting corruption
John Githongo resigned on Monday while in the UK and has not spoken in public.
Gladwell Otieno, who succeeded Mr Githongo as head of the Kenyan branch of Transparency International, said: "It appears his life is threatened".
President Mwai Kibaki was elected in 2002 on a pledge to clean up Kenya but diplomats say that "massive looting" is still going on.
Following Mr Githongo's resignation, the US announced it was suspending funding for Kenya's anti-corruption efforts.
European Union diplomats are due to announce whether they are taking similar steps.
Is Kibaki still committed to fighting corruption?
Ms Otieno said that Mr Githongo had taken a lot of personal risk during his fight against corruption.
"You cannot prevent people from continuing to earn billions of shillings illegitimately without expecting some short of backlash," she told the BBC's World Today programme.
She said she had spoken briefly to Mr Githongo since his resignation and that he felt the government, and President Kibaki, was no longer committed to stopping corruption.
Mr Githongo, a former head of the Kenyan branch of watchdog Transparency International, was appointed just a month after Mr Kibaki's inauguration, to oversee his fight against corruption.
"Another strong, independent and effective anti-corruption crusader must be appointed immediately in order to restore international donor confidence in the current government," said the US ambassador to Kenya William Bellamy, shortly before announcing that the US would stop funding Kenya's anti-corruption efforts.
Donors initially welcomed Mr Kibaki's efforts to stamp out corruption and restored aid, which had been cut off under former President Daniel arap Moi.
But some diplomats estimate that Kenya has lost some $1bn in corruption over the past three years.
A Transparency International survey of perceived corruption rated Kenya 122nd out of 133 countries in 2003.
Meanwhile, an inquiry is continuing into the "Goldenberg affair", in which Kenya lost up to $600m between 1990 and 1993 in payments for non-existent gold.
Mr Moi has denied accusations that he was involved and has resisted attempts to appear in person.