A few nights ago Tuan Mohamed Saleh Nona Faris heard a rustling outside her house and saw a shadow move.

"He looked like a gorilla, he was completely covered in black from top to toe. I couldn't see his face or hands," the elderly lady in the west coast fishing district of Puttalam said.

She believes the intruder was one of Sri Lanka's notorious "grease devils".

Over the last few weeks large swathes of the country have been gripped by a fear of nocturnal prowlers who have frequented rural areas assaulting women at night.

The media and the public were swift to dub the intruders "grease devils". This is an old caricature referring to malevolent men who smear themselves in grease to avoid being caught.

But this wave of violence has spawned a series of brutal retaliatory vigilante attacks. People have been killed, there have been arrests by the hundred and tanks have been deployed.

There are conspiracy theories: villagers blame the security forces for launching and even fostering the grease devil assaults. They deny the charges, but violence has continued unabated.

It is a confusing situation in a febrile atmosphere - and no-one has got closer to working out who is actually behind the wave of assaults.

And there appears to be an ethnic dimension too: almost always, those reporting attacks from "grease devils" have been Muslim or Tamil rather than from the majority Sinhalese community.