Expert airs grim theory in search for missing Ballarat mother Samantha Murphy

Police probably suspect someone involved in the search for Ballarat mum Samantha Murphy could be her killer, a respected crime expert has said.

The 51-year-old mother of three left her Eureka Street home in Ballarat on February 4 to go jogging in Woowookarung Regional Park.

Despite major search efforts by the missing persons team, specialist commands and hundreds of Ballarat residents, Ms Murphy has not been seen since.