Thomas Sørensen, the Danish father involved in a drawn-out custody battle involving his five-year-old son Oliver, made a surprise appearance in a court in the Austrian city of Graz today for the start of a criminal trial against him.

Last Friday, a court in Helsingør upheld Sørensen's full custody of Oliver, but the legal battle continued in Austria today, where Sørensen faces up to ten years in prison on charges of unlawfully imprisoning Oliver.

The custody case has been going on since 2010, when Oliver’s Austrian mother, Marion Weilharter, who held sole custody of Oliver at the time, left Denmark for Austria and took her son with her. A Danish court later gave Sørensen custody of Oliver while an Austrian court did the same for Weilharter.

Sørensen is accused of going to Austria on April 3 of this year and taking Oliver out of the car belonging to Weilharter while she was dropping her son off at kindergarten. A co-conspirator held Weilharter down while Sørensen grabbed Oliver and subsequently drove him back to Denmark.

Sørensen and Oliver went into hiding and efforts by Austrian authorities to have him extradited on criminal charges were rejected by the Danish Justice Ministry on June 11. In August, Austrian authorities charged Sørensen with unlawful imprisonment. That trial began today in Graz.

There was speculation that Sørensen would not appear before the Austrian court, but according to his spokesperson, Janus Bang, Sørensen decided to attend after he was assured that he would be allowed to return to Denmark after giving his statement. There is still a chance, however, that the Austrian judge could imprison him.

“There is a minimal risk that the judge will decide to imprison him, because it is a criminal case with a sentence limit of up to ten years,” Bang told TV2 News.

Bang indicated that his client, who has an Austrian lawyer, believes that he is innocent and thinks he has the authority of the Danish courts behind him.

Austrian prosecuting attorney Gertraud Pilcher argued today in Graz that Sørensen took the law into his own hands when he took Oliver from Austria and that the criminal case is not about the custody dispute.

According to Austrian media, following the Danish court ruling on Friday, Weilharter had not expected Sørensen to make an appearance in court today. She will also provide testimony in the case and continues to challenge the Danish custody ruling.

“My move back to Austria was never illegal and I have never violated parental custody. The court's decision in Denmark was wrong and lacked reasoning,” Weilharter told TV2 News. “Denmark should have never given anything to Thomas Sørensen, who never had any kind of custody. Oliver isn’t even a Danish citizen.”

Weilharter also said that Oliver had been extremely traumatised by the situation.

This story was corrected on 26/9/12 at 12:52. We erroneously indicated that Oliver is receiving psychological help. He is not. We have also clarified that at the time that Marion Weilharter took Oliver to Austria in 2010, she had full legal custody of her son.

Oliver timeline:

July 2010: Marion Weilharter, Oliver’s mother, moves to Austria with Oliver against the will of the boy's father, Thomas Sørensen.

2010-2011: A Danish court grants Sørensen full custody while an Austrian court grants full custody to Weilharter.

3 April 2012: Sørensen takes his son from Weilharter when she delivers him to a kindergarten in the Austrian city of Graz. Austrian police issue an arrest warrant for Sørensen.

4 April 2012: The Sørensen and Oliver reach Denmark and go into hiding. Austrian police contact the Danish police.

7 April 2012: Austrian media indicate that Sørensen and Weilharter are in contact with each other.

17 April 2012: Austrian authorities ask the Danish authorities to deliver Sørensen after a European warrant is issued for his arrest.

11 June 2012: The Danish Justice Ministry refuses to extradite Sørensen to Austria, arguing that he has not done anything illegal per Danish law.

21 September 2012: A Helsingør court rules that Oliver should live with his father in Denmark.

25 September 2012: An Austrian court begins a criminal case against Sørensen, who, surprisingly, is present.