By Deepa Babington

PERUGIA, Italy (Reuters) - American student Amanda Knox was a naive young girl wrongly imprisoned for murder because of a botched police investigation and a tireless campaign to paint her as a monster, her lawyer told an Italian court on Thursday.

Knox is appealing a 2009 verdict that found her guilty of murdering her British roommate Meredith Kercher during a drug-fueled sex game that went wrong. Kercher's half-naked body was found in 2007 in a bloody pool in the apartment the two shared.

The Seattle student was sentenced to 26 years behind bars.

Her Italian boyfriend, Raffaele Sollecito, and an Ivorian drifter were also jailed over the murder. But much of the focus in the case has been on Knox, who prosecutors allege led the sexual assault and held the knife that slit Kercher's throat.

Wrapping up the defense case, Knox's lawyer Carlo Dalla Vedova pointed to errors in the probe by police and urged a panel of lay and professional judges to look beyond the image of Knox created by the media and the prosecution.

"She was a girl who was quite different from how she has been depicted," he told the court. "How many times have we heard Amanda Knox saying 'Why don't they believe me?'"

Knox, wearing a silver-gray top on Thursday, has visibly lost weight since her last trial and has appeared frail in her latest appearances in court.

A verdict in the trial could come as soon as Monday, with the Knox family optimistic their daughter will walk free from an Italian prison that has been her home for nearly four years.

Their hopes have been boosted by a forensics review that criticized traces of DNA found on a kitchen knife and Kercher's bra clasp -- evidence that was used to convict Knox -- and attacked police for sloppy handling of crime scene material.

But prosecutors have since tried to wrest back momentum in the case by focusing on other evidence pointing to Knox and targeting her personality, painting her as sex-crazed girl who resented her roommate and enjoyed flirting with danger.

They allege Knox and Sollecito staged a theft in the Perugia apartment to throw police off track and have attacked Knox's credibility by pointing to her false accusation blaming a Congolese barman for the murder.

Knox says she wrongly accused the barman in a moment of panic while under police questioning. In one particularly sharp attack earlier in the trial, the lawyer for the barman called Knox Satanic, diabolic, a witch and a she-devil.

Defense lawyers have hit back, saying such extreme characterizations are part of a campaign by the prosecution and media to justify a lack of motive in the case by creating a false image of Knox.

Many supporters in the United States see Knox as an innocent student abroad, trapped by an unfair justice system. Her family regularly appear on U.S. talk shows and she is backed by a dogged Internet campaign.

The trial is expected to wrap up by Saturday or Monday at the latest, with Knox expected to address the jury before they decide her fate.