The 48-year-old man, identified only as Detlef S. in line with German privacy rules, is charged with 350 counts of sexually abusing minors in his care between 1987 and 2010, and with 35 counts of facilitating sexual acts with minors.

He faces up to 15 years in prison if found guilty.

The defendant began abusing his twin stepchildren, who are now 28, in 1987 when they were around four years old, according to the indictment.

He began molesting his daughter, who is now 18, when she was nine. On her 12th birthday, after all the other children had left her party, he forced her to have sex with him for the first time. After that, he continued to regularly sexually assault her, prosecutors told the court, the DAPD news agency reported.

Judge Winfried Hedge read aloud a letter written by his daughter saying: “you made my life a living hell.” Detlef S. sat still during the proceedings, showing little emotion.

No plea was entered as the trial opened, which is normal for German proceedings, but defense attorney Thomas Dueber read a statement in which the defendant admitted to being the father of his stepdaughter’s seven children.

Prosecutors said before the trial that DNA samples confirmed that. An eighth child died before DNA tests could be done.

The judge said prosecutors are also now investigating whether the suspect assaulted one of the daughters he had with his stepdaughter, who was born in 2004.

Attorney Katharina Hellwig, who represents the stepdaughter, said she had been hoping the father would confess so that her client would not have to take the stand and relate her story. Instead, judges cleared the courtroom of spectators and heard the stepdaughter’s testimony behind closed doors.

Stepson Bjoern B. left the trial after about an hour, appearing shaken. He told reporters he had heard “terrible stuff” in the courtroom but felt it was necessary to be there.

“I wanted to give my sister strength to go on with this,” he said. “We are in this together, and together we are trying to have the strength to live through this. It would make no sense to do this alone.” He and the other two alleged victims have joined the trial as co-plaintiffs, as allowed under German law.

Detlef S., a truck driver who lived with the family in the small town of Fluterschen, near Bonn, did not address the court himself. He has been in custody since August after his daughter came forward to authorities.

Outside the courtroom, Dueber said his client was not admitting the charges against him.

“He acknowledged paternity ... but paternity is not part of the indictment,” Dueber said. “He’s innocent until proven guilty.” Detlef S. is also accused of forcing his daughter and stepdaughter to have sex with other men for money. Two of those men also face charges and will be tried separately.

His trial resumes Wednesday, and a verdict could be handed down as early as the end of this month.

Germany’s Bild newspaper has called the suspect the “German Fritzl” — a reference to Europe’s most infamous case of incest. Austrian Josef Fritzl was found guilty in 2009 of locking his daughter in a dungeon for 24 years and fathering seven children with her. He is serving a life sentence.