The Alternative for Germany (AfD) party and other extremists have seized on the brutal killing of 14-year-old Susanna Maria Feldman in their campaign against Chancellor Angela Merkel's asylum policy.

The accused, rejected asylum seeker Ali Bashar, 22, faces his verdict in a hearing starting at 9:30 am (0730 GMT) in a heavily guarded court in Wiesbaden, the city where the murder took place in May last year.

If found guilty, Bashar faces a likely sentence of life in prison, and could be kept behind bars beyond the usual maximum 15 years if judge Juergen Bonk finds the crime to be of exceptional severity.

Prosecutors charge that Bashar battered, raped and strangled the schoolgirl to death in a wooded area near railway tracks on May 23.

He then allegedly sent false messages from Susanna's smartphone indicating she had left for an impromptu trip to Paris.

Her body was only found on June 6 in a shallow grave covered with leaves, twigs and soil.

By this time, Bashar and his family had left Germany and returned to Arbil in northern Iraq.

The accused was however arrested by Kurdish security forces and, even though Berlin and Baghdad have no formal extradition treaty, taken back to Germany.

- Incapable of empathy -

Federal police chief Dieter Romann personally joined the controversial operation, as newspaper front pages showed pictures of commandos escorting a heavily restrained Bashar off an aircraft.

Bashar later confessed the killing but denied the rape, claiming that he and the girl had consensual sex before she fell, got angry and threatened to call the police.

In a separate trial, Bashar is accused of twice raping an 11-year-old girl, who was believed to have also been sexually assaulted by an Afghan youth.

The Bashar case put renewed pressure on Merkel's government over the decision to keep open German borders at the height of Europe's refugee crisis.

The far-right has voiced fury about cases of sexual violence committed by those migrants and other foreigners -- including mass assaults in Cologne on New Year's Eve 2015-16, and, in April this year, the alleged gang rape by eight Bulgarian teens of a 13-year-old girl.

Bashar, his parents and siblings arrived in Germany in 2015, at the peak of the influx that would bring more than a million asylum seekers, mostly from the Middle East and Africa.

His asylum request was rejected in late 2016, but he obtained a temporary residence permit pending his appeal.

During this time, he came to police attention for fights, alleged robbery and possession of an illegal switchblade.

Susanna's mother, dressed in black during the almost four-month-long trial, broke down in tears as the court heard the harrowing details of the crime.

Bashar by contrast appeared composed during the trial, in which a psychiatrist testified the accused has a personality disorder and is incapable of empathy.