Missing librarian Julie Ann Garciacelay.

One of Melbourne's most enduring mysteries was on Wednesday declared by a coroner to be a murder case and missing persons detectives will now kick-start a review.

It was a little over a week before librarian Julie Ann Garciacelay’s 20th birthday when she disappeared from the flat she shared with her sister in Canning Street, North Melbourne, on July 1, 1975.

Police long suspected Ms Garciacelay, who had moved from California eight months earlier, was murdered and on Wednesday, State Coroner Sara Hinchey confirmed their suspicions.

“Despite there being no evidence as to the exact circumstances and cause of Ms Garciacelay’s death, her death was the result of homicide,” Ms Hinchey found.