Kirk Reid was free to attack women for four years after becoming a suspect
Police officers who made blunders in two serial sex attacker inquiries could be prosecuted, the Independent Police Complaints Commission has warned.
London street stalker Kirk Reid, 44, and taxi-driving rapist John Worboys, 51, were jailed earlier this year.
Police were criticised for inaction, bad decisions and failing to link offences in both investigations.
The IPCC is now investigating 14 officers, including a superintendent, and could press charges.
Reid was jailed for life after attacking 27 women on the streets of south London.
Following his conviction it emerged that police had identified him as a suspect four years previously - but taken no action.
Worboys was locked up indefinitely for drugging and raping female passengers in his black cab.
But police had not linked up several of his attacks - while officers simply did not believe some of the victims because they had been drinking alcohol.
Seven officers from each case have now been given notification they are being investigated.
It is thought the IPPC inquiry, due to be published before Christmas, will heavily criticise police tactics in sex crime investigations.
The Metropolitan Police has already changed the way it tackles sex crimes in light of the cases.
Individual borough's Sapphire teams have been brought under the control of a central unit.
A Metropolitan Police spokesman made no comment.