Police failed to examine CCTV footage of a vehicle behind a bus shortly before an 18-year-old girl was run over twice, the Old Bailey heard.
Kate Sheedy, then 18, was seriously injured in the incident
Kate Sheedy, then aged 18, was hit near her home in Isleworth, west London, in 2004 and badly injured.
She said she was hit by a white people carrier with blacked-out windows.
Levi Bellfield, 39, of west London, denies her attempted murder and the murders of students Marsha McDonnell and Amelie Delagrange.
He also denies attacking two other women.
Detectives investigating the incident involving Ms Sheedy examined security camera footage taken from a nearby pub, the County Arms.
Although six tapes were seized, only three were examined by an officer in the case.
The footage showing a white vehicle following the bus Miss Sheedy was on was not examined and only seen when a review of the case was carried out some time later, the court heard.
Det Sgt Philip Royan said: "The relevant part wasn't examined."
The jury also heard from a motorist Philip Lancaster, who saw a man he later identified as Mr Bellfield in a white Toyota Previa with blacked-out windows the day before the attack.
French student Amelie Delagrange, aged 22, and gap year student Marsha McDonnell, 19, died after being struck on the head with blunt objects.
The attacks were carried out in south-west London between October 2001 and August 2004.
The trial continues.