A former Serco executive who oversaw custody contracts that are at the centre of a police inquiry has become a director of another company that also services Ministry of Justice contracts.
Paul Rennie was Serco's head of custody services in London and the east of England from December 2011 to August 2013.
Serco has since found evidence in those regions that prisoners had been recorded as delivered ready for court when they were not.
Rennie left Serco in the same month as the MoJ began investigating a possible fraud worth up to £40m and called in detectives from City of London police.
He is now business development director at Taylormade, a security firm that is being subcontracted work by Serco from the prisoner escort contract.
There is no implication that Rennie has done anything wrong, but both he and Serco do not wish to comment on why he left. Rennie says that he may be called as a witness in any subsequent criminal prosecution.
Margaret Hodge, the chair of the Commons public accounts committee, said she would like both Rennie and the company to be open about his role because a firm in which he is involved is profiting from the same prisoner service contract.
"We have got to get answers to key questions as to why Paul Rennie left Serco and why he jumped just before a police investigation was launched, especially since he has since turned up at another company which benefits from similar contracts.
"At the very least this looks bad and it makes a case yet again for complete transparency where the taxpayer's money is involved."
The development comes after the release of a highly critical report into Serco's custody services in the east of England.
The chief inspector of prisons, Nick Hardwick, found that "persistent and pressing" staff shortages adversely affected people held in privately run court cells across Cambridgeshire and Essex.
In August, the MoJ put Serco's £285m prisoner escorting and custody services (PECS) contract for London and the east of England under administrative supervision and called in police. Rennie left the firm earlier that month, according to his LinkedIn page.
"Interim audit findings suggest that some Serco staff have been manipulating their performance figures to show enhanced performance against this measure," the MoJ said in a statement.
The firm has said it will repay £2m of profits on the contract for transfers in London and East Anglia since 2011.
Taylormade was given a contract by Serco in April 2013 to provide medical services in support of its prisoner escort contract.
Serco also brings in custody officers from Taylormade on a temporary basis to meet high demand or fill vacant posts on the prisoner escort contract.
Taylormade is also an approved Home Office contractor, providing emergency medical cover and support staff on deportations.
The firm's website states that Taylormade is "the sole medical provider to the Home office for repatriation of illegal immigrants and failed asylum seekers".
Rennie declined to answer the Guardian's questions about why he left Serco and whether it was appropriate for him to be working for a sub-contracted firm, saying he does not wish to prejudice any subsequent criminal prosecution.
"I am aware there has been a police investigation by City of London police. I do not know whether that is still ongoing.
"If it is, I would not wish to respond to your questions. If proceedings are brought against anyone, and I have no information whether or not they might be, I am conscious of the possibility that I may be asked to be a witness," he said.
"I have not recruited detention and custody officers and prison escort officers for Taylormade."
Serco would not disclose if any staff have left the company over the fraud allegations.
A spokesman told the Guardian: "There have been a number of management changes both within the PECS contract and the wider business as a result of Serco's corporate renewal programme and internal restructure.
"This programme of renewal was positively assessed by the Cabinet Office at the end of January 2014."
Frances Crook, the chief executive of the Howard League for Penal Reform, said: "It is worth asking what corporate renewal means when managers can disappear then resurface as subcontractors."
Regarding the report by the chief inspector of prisons, Serco's partnership director, David Holdsworth, said: "While we are pleased that inspectors found our staff had good interpersonal skills and were courteous to detainees, we accept that there have been some staffing issues across Cambridgeshire and Essex and that there is room for improvement."