A NSW Central Coast man accused of murdering his former girlfriend became the sole focus for police who failed to adequately investigate other evidence, a court has been told.
James Scott Church, 51, has pleaded not guilty in the NSW Supreme Court to murdering Leisl Smith, 23, who vanished on August 19, 2012.
Her body was never located but her car was found abandoned at Tuggerah railway station more than a month after she disappeared.
Ms Smith told a number of people she claimed to be carrying Church's baby, including his partner Belinda Lees.
Church's lawyer Manny Conditsis in his opening address at the judge-alone trial on Wednesday said there were no issues his client told some lies after she disappeared.
But by his third interview, "the police investigation became single-minded against the accused," Mr Conditsis said.
"And that single-mindedness has led to potentially important if not vital evidence not being before the court."
The defence case is that Ms Smith's former partner Craig Elkin was a viable suspect.
Witnesses are expected to testify that the late Mr Elkin threatened to kill Ms Smith if she ever entered into another relationship or became pregnant to another man.
Mr Conditsis said Ms Smith was known to have interactions with "bikies" who could have also been involved in her killing.
He also disputed the Crown's submission that Church wanted his relationship with Ms Lees to "flourish" and financially benefit from her wealthy parents.
"This motive is lacking in any substance and is speculative," he said adding that Ms Lees' father was a lawyer, well versed in prenups and the like.
While Church was the last person to see Ms Smith when he says he dropped her south of Wyong, the "penultimate person was Mr Elkin", he said.
Justice Elizabeth Fullerton is also open to finding that Ms Smith "does not want to be found" and is alive, or was for some time, she was told.
The Crown says Ms Smith's claims of carrying Church's child "fed into his motive to kill her," as well as his desire to save his relationship.
Prosecutor Kate Ratcliffe said Church picked up Ms Smith from the station in his white ute after arranging to meet her on August 19, as part of a premeditated plan to murder her.
Two days earlier he allegedly drove to remote locations to find a suitable spot to dispose of the woman's body.
The judge expects to hear evidence from Ms Lees about allegations Ms Smith made to her against Church.
They included that he had kicked her dog, was an alcoholic and had been violent to an ex-partner.
But following reassurance from Church, Ms Lees is expected to say she believed Ms Smith was a "crackpot" and dismissed her claims.
The trial continues.
