Kirk Reid was free to attack women for four years after becoming a suspect
The Metropolitan Police (Met) has been criticised for staffing a unit to catch rapists with under trained officers.
It has emerged that 112 out of 349 staff joined on temporary six-month contracts and will receive training only if they choose to stay.
The Met Police Authority said it was concerned by the lack of trained officers.
The Met said it wanted to get the unit running as soon as possible and training will be offered in due course.
The £1.3m unit in Lewisham, south-east London, will not be fully up and running until next April.
It was designed to improve the force's response to sex crimes after a series of bungled inquiries.
Senior officers were criticised for leaving untrained officers to investigate the crimes of taxi driver rapist John Worboys and street stalker Kirk Reid.
Independent investigators are also examining why the force took so long to connect sex attacks with strikingly similar features.
Valerie Brasse, a member of the Metropolitan Police Authority, said although all those seconded to the unit will be fully-fledged detectives, some will have had no experience investigating rapes.
Officer had not linked several of Worboys' attacks
Mrs Brasse said: "Given the reasons for setting it up, that seemed a rather uncomfortable place to be."
Earlier this year senior officers decided to bring regional sex crime units, known as Sapphire teams, under the umbrella of one central command.
Senior officers want the unit to become a centre of excellence that handles an additional 4,000 sex crimes every year.
Discussions are under way to bring in a team of specialist prosecutors to handle cases as they are brought to court.
A Met spokesman said: "Due to the quick time-frame for the implementation, there was always going to be a bedding-in period for all the changes to come into effect.
"Getting 400 staff put through a new training course was never going to happen instantly.
"However, this is being progressed as quickly as possible with priority being given to permanent members of staff, as you would expect."