Luke Peter Joseph Coughlan, 43, appeared in the County Court on Wednesday where he pleaded guilty to 11 charges, including grooming a child under 16, sexual penetration of a child under 16, and knowingly possessing child abuse material.

The court heard in 2009, Coughlan started talking with a 13-year-old American girl on the online chat site Omegle.

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The conversations became sexual and Coughlan told the teenager to engage in degrading sexual acts while on a video call with him.

He also told the girl to send him more than 200 naked photos and videos. In some of the images, Coughlan instructed the girl to write messages like, "I belong to Luke", on parts of her body.

In October 2013, Coughlan flew to the United States to see the girl. He met up with her in a motel room where he video taped the sexual abuse.

The court heard in 2017, Coughlan started chatting online with a 14-year-old girl from northern Victoria. She agreed to meet with him in February of that year.

Coughlan rented a motor home and drove to a park near her house where he sexually abused the girl.

There were a number of interactions between the teenager and Coughlan from February 2017 to October 2019.

The court heard he instructed the girl to take and send more than 300 sexually explicit images and videos.

The images were degrading in nature and involved self-harm. He also instructed the girl to write his name on her naked body.

The court heard during a pretext phone call between Coughlan and the girl in October 2019, Coughlan made admissions to the offending.

Police searched Coughlan's Westmeadows property the next day. He was arrested and taken to the Broadmeadows Police Station where he made a no-comment interview.

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A search of his electronic devices revealed there were another three victims.

One of the victims was a 14-year-old girl from Western Australia, who Coughlan had been contacting online in 2017.

After some time, Coughlan began asking the girl for more than 200 sexually explicit photos and videos.

The court heard the girl believed she was in a relationship with Coughlan but she soon realised he was just using her for his own sexual gratification.

When the girl tried to stop contacting Coughlan, he threatened to kill himself.

In September 2018, Coughlan travelled to Western Australia to meet the girl. Coughlan knew where the girl lived, despite her never telling him her address.

The court heard Coughlan drove to her house and waited in his car, begging her to come outside to him. She refused to leave her home and Coughlan eventually left.

The court heard the girl was "scared for her life".

There were two other girls from the United States and Canada that Coughlan contacted via online chat services.

He instructed the girls to send him child abuse material, including videos of them performing degrading sexual acts. The court heard he also instructed the girls to call him "daddy".

More than 230 images and videos of the girls were found on Coughlan's electronic devices. Detectives also found more than 1000 images and videos of unidentified underage girls.

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A statement from the northern Victorian girl was read to the County Court on Wednesday.

In the statement, the girl said Coughlan had "turned (her) world upside down" and she now struggled to form meaningful relationships.

Defence counsel Martin Kozlowski told the court Coughlan's failed attempt to become an air traffic controller led to him contacting the first girl.

The defence counsel said Coughlan formed what he believed was a romantic relationship with the victim.

Mr Kozlowski said a psychological report tendered to the court showed Coughlan did not have a "specific attraction" to underage girls.

The defence counsel said the victims had "mature" bodies and Coughlan was instead interested in the bondage and control elements of the interactions.

Judge David Sexton said that submission "troubled" him and he was concerned about the "glaring gap" in the psychological material.

The judge said he needed a further assessment to determine why Coughlan committed the offences, so he could evaluate the 43-year-old's risk of reoffending.

Judge Sexton said the crimes were "extremely serious" and Coughlan was facing a "fairly significant term of imprisonment".

Coughlan was remanded in custody so he could undergo a Forensicare assessment. He is due to return to the County Court in July.

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