The tiger, which swam across the Bhramhaputra from Orang National Park in Udalguri district to take shelter between Morigaon and Nagaon districts, killed a 38-year-old woman, police said.
When sub-inspector Tilak Chandra Bora and his team went to nab the tiger, it pounced on him in a paddy field, injuring the policeman critically, they added.
The tiger was finally shot dead to save the sub-inspector.
The feline had also injured two villagers and killed a bull in the past few days.
Forest officials, veterinary experts and activists from a prominent animal rights NGO Aranyaak arrived at the site and were investigating to the incident.
In the last week alone, four tigers have died in Assam. (With PTI Inputs)