Experts are investigating the first confirmed stranding of an orca in England and Wales for almost 20 years, the Zoological Society of London (ZSL) said.
The juvenile male killer whale, approximately 15ft long, became stranded in salt marsh off the coast of Norfolk and Lincolnshire.
It is the first confirmed orca stranding that the Cetacean Strandings Investigation Programme, of which ZSL is a partner, has investigated in England and Wales since 2001.
Orcas are a priority species for research by ZSL. This is because they are top predators which can absorb significant concentrations of marine pollutants, such as chemicals known as PCBs. These substances accumulate as they go up the food chain.
ZSL's Rob Deaville and Matt Perkins collected blubber, liver, muscle and kidney samples from the marine mammal. The orca was internally mostly intact despite it having probably died weeks ago.
Tests will analyse the samples for marine contaminants, while genetic analysis will help determine which population the animal came from. The teeth have been collected to accurately assess the whale's age.
The experts said there was no evidence of recent feeding as its stomachs were largely empty.
The team found a large fragment of plastic in the first stomach, though it had not killed the orca as the stomach was not blocked.