Its closest challenger in the 9pm-10pm slot was BBC One programme 'Traffic Cops', which earned 4.5 million viewers.
This gave ITV1 a 24.1% share of viewing and its state-owned rival 16.5%.
'The Red Dahlia' concludes tomorrow at 9pm when it is up against BBC One stalwart 'New Tricks'.
Channel 4 managed 2.6 million viewers (including the ratings for Channel 4+1) and a 10.6% share with the semi-final of Gordon Ramsay's competition to find Britain's best independent local restaurants in 'The F Word'. The final is tomorrow, also at 9pm.
'Celebrity Big Brother', followed 'The F Word' and scored 3.2 million viewers and a 19.2% share between 10pm and 11.15pm.
Back at 9pm, BBC Two started three-part series 'History of Now: The Story of the Noughties' with 1.6 million viewers and a 5.9% share.
It was enough to beat Five's showing of a 'CSI' repeat, which was watched by 1.2 million viewers and gave the channel a 4.4% share.
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