Bengal marsh mongoose?

Description:

Around 3-4 feet long animal, with a long tail, almost as big as its body. Held its tail upright while walking. Seemed black with a shiny coat in florescent light. Eyes shone in night.

Habitat:

Banks of a tributary of Hoogly river. The banks are a marshy canal.

Notes:

Spotted a couple at midnight, on the upper branches of a flowering tree. Were not very quick animals. There were atleast two, but could have been four. Used low branches of trees along the canal of a river to navigate through the forestry.