"We did ask the Chinese to hold an investigation and we are pleased they are now doing that and I stand ready to cooperate in any way we can," Mr Cameron told reporters in Indonesia during a tour around Asia to promote business.
"It's very important we get to the bottom of what happened in this very disturbing case," he added.
China's official Xinhua news agency said evidence from a reinvestigation of the death of businessman Neil Heywood indicated he had been murdered and named Gu Kailai, wife of senior Communist Party politician Bo Xilai, and an assistant in their household as suspects.
Mr Heywood, 41, was found dead in a hotel room in Chongqing, central China, last November.
The Communist Party has suspended Mr Bo from its Central Committee and its Politburo.
With a once-in-a-decade leadership handover months away, the Communist Party's elite must confront the first very public turmoil at the centre of power in more than 20 years.
President Hu Jintao and other leaders face a quandary – how to prevent rifts among the leaders even as they manoeuvre for gain from Mr Bo's dismissal from the Party's Central Committee and its Politburo.
The case has exposed divisions within the ruling elite. Sources close to the leadership said these were often ideological, and overlapped with open feuding between left-wing and liberal groups.
Left-wing supporters of the charismatic Mr Bo defended him as the instigator of a much-needed new and improved path for China. But those pushing for his fall were alarmed by his sweeping crackdown on organised crime, which brought allegations of widespread abuse of power.