This is the room where my whole family was killed, says Safa Younes.

Bullet holes pepper the front door to the house in the Iraqi town of Haditha, where she grew up. Inside the back bedroom, a colourful bedspread covers the bed where her family was shot.

This is where she hid with her five siblings, mum, and aunt when US marines stormed into their home and opened fire, killing everyone apart from Safa, on 19 November 2005. Her dad was also shot dead when he opened the front door.

Now, 20 years on, a BBC Eye investigation has uncovered evidence that implicates two marines, who were never brought to trial, in the killing of Safa's family, according to a forensic expert.

The evidence - mainly statements and testimony given in the aftermath of the killings - raises doubts about the American investigation into what happened that day, and poses significant questions over how US armed forces are held to account.

The killing of Safa's family was part of what became known as the Haditha massacre, in which US marines killed 24 Iraqi civilians, including four women and six children. They entered three homes, killing nearly everyone inside, as well as a driver and four students in a car, who were on their way to college.

The incident triggered the longest US war crimes investigation of the Iraq war, but no one was convicted for the killings.

The marines claimed they were responding to gunfire after a roadside bomb went off, killing one of their squad members, injuring two others. But Safa, who was only 13 at the time, tells the World Service: We hadn't been accused of anything. We didn't even have any weapons in the house.

In a shocking revelation, evidence suggests two marines may have been responsible for the shootings, as forensic expert Michael Maloney stated that two marines entered the room and shot at the women and children. His conclusion was based on the crime scene photos taken at the time and new evidence from testimonies.

Despite being charged initially, the marines involved faced no significant legal consequences. Squad leader Frank Wuterich was the only one to go to trial, but was found guilty only of negligent dereliction of duty, receiving a punishment described as a slap on the wrist by some legal experts.

As Safa Younes reflects on her past, she expresses disbelief that no marines have been held accountable for the deaths of her family. It’s as if it happened last year. I still think about it, she says, stressing that it has been nearly 20 years without justice.

As the investigation unfolds, Safa continues to call for accountability, seeking justice for her family and all victims of the Haditha massacre.