Defendant Detlef S (left) arrives for the start of his trial in the regional court in Koblenz, western Germany on Tuesday. He went on trial accused of sexually abusing his daughter and stepchildren for decades as neighbors and social services apparently ignored telltale signs. Torsten Silz Germ / Agence France-Presse

KOBLENZ, Germany - A German trucker admitted on Tuesday to fathering seven children with his stepdaughter but denied forcing himself on her, her brother and his biological daughter during an alleged 23-year ordeal.

The 48-year-old, identified only as Detlef S, went on trial in the western city of Koblenz, accused of raping his stepdaughter, now in her late 20s, over more than two decades and of brutally abusing his daughter and stepson.

Dressed smartly in a red jacket, blue shirt and colorful tie, S showed no emotion as the charges were read out and did not speak.

But his lawyer, Thomas Dueber, told the court: "He would like to clarify that he is the father of the seven children of the co-plaintiff (his stepdaughter). But he denies the charges made against him."

A verdict is expected on Feb 25. S faces 15 years behind bars if convicted. In line with German privacy laws, the defendant's full name was not given in court.

The stepdaughter, named in media reports as Natasha, told reporters as the trial opened: "I hope he gets the right sentence and that he can never hurt anyone again."

Paternity tests have proved with virtual certainty that the unremarkable man with glasses and graying, receding hair was the father of the seven children. An eighth child died shortly after birth and was not examined.

Several German media outlets have compared the case to that of Austrian Josef Fritzl, who held his daughter Elisabeth as a sex slave in a cramped dungeon for 24 years.

Fritzl raped Elisabeth thousands of times, fathering seven children with her and letting one of the newborn babies die. He was sentenced to life in prison in March 2009.

In total S is charged with 350 counts of sexual assault and grievous sexual assault of minors.

According to the charge sheet, S abused his biological daughter regularly from 12 onwards.

He is also accused of prostituting the stepdaughter and his biological daughter out to others at 40 deutschmarks and later 30-50 euros ($41-68) per time, allegedly while he watched.

He also used to beat all three with his belt or a homemade whip, public prosecutor Thorsten Kahl said.

It also emerged on the first day of the trial that there was a criminal investigation in 2002 but that it was abandoned because the daughter disputed the accusations against her father, while the stepdaughter said nothing.

The stepson, identified as Bjoern, told reporters outside the courtroom that authorities had failed to do their job properly and missed telltale signs of abuse in the house, alleged to have occurred between 1987 to 2010.

"If you are a trained social worker, you are supposed to go there and interview the victims without the perpetrator being present, and not all together," he said.

"It is clear that the children were unable to build up any trust of the youth welfare office."

The man was arrested on Aug 10, 2010, and has been in custody since.

The mother of the three, who is in her 50s, is expected to appear as a witness in the trial and prosecutors are not charging her with any offense, lawyer Katharina Hellwig said last week.

The trial, which has shocked Germany, follows several similar cases around the world.

Agence France-Presse