The mother of schoolgirl Alice Gross has told an inquest there are still "unanswered questions" over her death at the hands of a foreign criminal.
Latvian builder Arnis Zalkalns is believed to have murdered the 14-year-old from Ealing, west London, in a sexually motivated attack before taking his own life.
Zalkalns had previously served a prison sentence for killing his wife in his native country and Ros Hodgkiss, Alice's mother, said the family "remain stunned" he was able to come to the UK.
"It is impossible to express the devastation that we still feel at Alice's death," Ms Hodgkiss said, reading from a statement.
"We have many unanswered questions. We will never know exactly what happened on that day."
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Coroner Dr Fiona Wilcox ruled last year that the inquest, being held at the Royal Courts of Justice in London, would examine whether failures by the British Government and police contributed to Alice's death.
Ms Hodgkiss said the family was "extremely grateful" that possible failures were "going to be explored".
"We want to reiterate that the reason for these questions is so that we can establish whether or not the systems for monitoring foreign offenders and cross-border sharing of information are robust," she said.
"We appreciate that they may have changed significantly, but we remain stunned that a foreign national with a conviction for murder was not monitored, or even known about in any way.
"This has destroyed much of our faith in our country's ability to protect its citizens.
"The Home Office and the police forces nationwide should be doing everything they can to ensure that this should not be allowed to happen again."
Ms Hodgkiss said her daughter was "witty, smart and academic but she could also push boundaries".
"In this way she was no different to any normal teenager," she said.
"She was independent and like many teenagers of her age she enjoyed shopping, cinema and attending parties with her friends.
"She could also at times be shy and under-confident and she cared a lot about what other people thought of her."
Alice's body was found in the River Brent, tied up and weighted down with bricks, logs and a bicycle wheel, a little over a month after she went missing from home.
Pathologist Ashley Fegan-Earl told the inquest that "compression asphyxiation" was the most likely cause of death.
Zalkalns was found dead in a park less than a week after Alice's body was found and police said he would have been charged with murder had he not died.