Levi Bellfield's partner did not believe he had killed schoolgirl Milly Dowler, the Old Bailey heard today.
Emma Mills said she did not contact police about his "disappearance" on the day the 13-year-old went missing, or his subsequent quip: "What, do you think I've done Milly?"
She had not mentioned Milly Dowler until after Bellfield's arrest in November 2004.
Asked by defence counsel Jeffrey Samuels QC why she did not "harbour any suspicions", Miss Mills, 33, said: "I didn't think he'd done it, but when he made that comment it made me think 'Why did he make that comment?'. But I didn't think that he had done it."
The mother of Bellfield's three children was giving evidence for the second day against her partner of nine years.
Bellfield, 43, denies abducting and murdering Milly and attempting to kidnap 11-year-old Rachel Cowles in March 2002.
Milly disappeared "in the blink of an eye" after leaving Walton-on-Thames station, in Surrey, to walk home.
The prosecution claims Bellfield was living yards away and murdered Milly in his flat before dumping the body. Six months later, her remains were found in woods 25 miles away.
Bellfield, a former wheelclamper and bouncer, was convicted in 2008 of the murders of Marsha McDonnell, 19, and Amelie Delagrange, 22, and the attempted murder of Kate Sheedy, 18.
Miss Mills was asked what her response was to the remark about Milly.
She said: "I asked how he could make a joke like that. I didn't say much... disgusting."
Miss Mills said when she found bedding missing at the flat in Walton, she "thought he had disappeared with a woman in my bed".
She denied defence suggestions that their move from Collingwood Place had been planned because it was damp, or because Bellfield had been running a credit card scam.
Eight days after Milly vanished, Bellfield told her the red Daewoo Nexia car they had been using was stolen.
The trial was adjourned to tomorrow, when Miss Mills will complete her evidence.