A woman was brutally beaten and strangled to death by a 17-year-old after laughing at him during sex, court has heard.

Blanca C., 28, met Mohamed Ali S., 17, in a bar in German city Frankfurt on October 3 last year, where the pair consumed a few drinks and drugs together, according to prosecutor Constanze Jung.

'Then they left [the bar] to go to her flat and wanted to have consensual sex,' Jung told German tabloid Bild. 

But when Mohamed reportedly failed to get an erection, Blanca laughed at him for it.

This enraged the Tunisian teenager who 'hit her, choked her and throttled her' in a violent frenzy until she died, Jung said.

Blanca C. (pictured), 28, met Mohamed Ali S. in a bar in German city Frankfurt on October 3 last year, where the pair consumed a few drinks and drugs together, according to prosecutor Constanze Jung

The defendant allegedly filmed part of the attack on his phone. As he angled the camera at Blanca's body, he boasted: 'I killed her', according to the prosecution.

A witness called the police in the middle of the night, who rushed to Blanca's apartment, where they broke down the door to find her dead. 

Mohamed Ali S. was arrested in his parents' home in Frankfurt's Bonames district - about 6 miles from Blanca's flat - just hours later.

'She was such a happy, young woman,' a neighbour told Bild about Blanca, who reportedly loved going out and was full of life. 

Another said Blanca's devastated mother, who lives in the flat right next to her daughter, made a 'B' with pink and purple tea lights in front of Blanca's door the day after her death.

Blanca's mother wrote on Facebook: 'My love, my happiness, my joy, my EVERYTHING has gone to the Garden of Eden.' 

The murder trial, which is closed to the public due to the defendant being a minor, started at the Frankfurt District Court in the German state of Hesse on Monday. 

Mohamed Ali S. could get a prison sentence of up to ten years under German juvenile criminal law if he is convicted.