They believe the attack was carried by some of the men she intended to write about in the northern France port.
Today detectives were rounding up potential witnesses, who include some of the 500 odd vagrants sleeping rough as they attempt to board ferries or trains to the south coast of England.
The victim, who cannot be named for legal reasons, was described as “a London student who had travelled to France to highlight problems surrounding clandestine immigration.”
A local police spokesman added: “She appeared to be working alone, which was clearly a very dangerous thing to do.“We fear that the men she was reporting on attacked her in the wood where they were staying.”
The woman is believed to have wanted to spend time with the immigrants in a notorious makeshift camp called “The Jungle” before the attack happened on Tuesday night.
Others in the town said she was in her late 20s or early 30s, and taking her own photographs rather than working with a colleague.
"The Jungle” is part of a disused an industrial zone called The Dunes, a short walk from the ferry port.
There, would-be immigrants make tents out of plastic sheets and build fires. They are supported by local charities, with the newly elected Right Wing council in Calais refusing to provide them with permanent accommodation.
Father Jean-Pierre Boutoille, of the refugee charity C’Sur, said: “There are lots of journalists, including students, who come here to get to the heart of what’s going on, to write reports and produce films.......
Most of the vagrants claimed to be from Iraq, Afghanistan, or the Middle East, although police believe many were from eastern Europe and the Balkans.