All three suspects in the murder of British student Meredith Kercher are to remain behind bars, a judge has ruled.

American university student Amanda Knox, her Italian ex-boyfriend, Raffaele Sollecito and Ivory Coast national Rudy Hermann Guede have all had their request for release refused.

The news comes just hours after Kercher's parents said they were shocked and distressed after pictures of their daughter's bloodied corpse were shown on Italian television.

Rome-based journalist Nick Pisa said scientific footage showing the 21-year-old's body was broadcast last night as part of a documentary on the murder made by a small station in southern Italy.

"They are gruesome images. You can see the wound which was inflicted on her throat," he told Sky News.

"The Kercher family lawyer has released a statement, reserving the right to take legal action against the television station."

Kercher, an exchange student from Leeds University in England, was found with her throat cut in the apartment she shared with other students in Perugia, Italy.

Three suspects held in Italy in connection with the murder have been making final appeals to be freed from prison.

Journalist Nick Pisa said the controversial documentary in question was made by a television station based in the region where one of the suspects — Rafael Sollecito — is from.

Called "Perfect Crime" or "Imperfect Investigation," the program looked at anomalies in the police investigation into the killing.

Criticism of the Italian police has also come from Sollecito's lawyers, a fact which the Kercher family lawyer said was of interest.