Two directors answer directly to the head of operations - one in charge of government investigations and the other overseeing allegations of corruption in the private sector. The former would have been perfect to step into Li's shoes - only he was also about to retire.

A succession committee was set up which concluded the director in charge of private sector investigations, Rebecca Li Bo-lan, did not have the necessary experience at senior level.

She had only been serving at that rank for six months.

The succession committee decided there was no one within the agency experienced enough to take on Li's role, so they sought out Ryan Wong Sai-chiu in retirement - the previous director of government investigations.

Peh told the committee that written into the terms of Wong's three-year contract is the requirement that he mentor the two directors under him as possible successors.

Peh added that the turnover rate in the last five years had been stable and that most of the staff who leave were at junior level.

The turnover rate in 2007 was 9.3 per cent; 7.8 per cent in 2008; 5.1 per cent in 2010; 6.3 per cent in 2011; and 5.6 per cent in 2012.

Peh said retaining staff at officer level was its toughest challenge. It lost 45 officers in 2009.

ICAC said officers at that grade were employed on a contract basis and therefore had "a higher propensity to shift jobs".

Asked by a lawmaker if the private sector was luring away ICAC officers with more lucrative salaries, Peh insisted the high turnover was not seen every year.

Legco recently approved funding for an assistant director of operations to help handle the Sun Hung Kai Properties inquiry.