Two Star Wars fans are in a critical condition in hospital after apparently trying to make light sabres by filling fluorescent light tubes with petrol.
Revenge of The Sith is the sixth Star Wars film to be released
A man, aged 20, and a girl of 17 are believed to have been filming a mock duel when they poured fuel into two glass tubes and lit it.
The pair were rushed to hospital after one of the devices exploded in woodland at Hemel Hempstead, Hertfordshire.
A third person present at the incident had been questioned, police said.
A videotape was found nearby by police called to the scene on Sunday.
A police spokeswoman said the pair were taken to West Herts Hospital before being transferred to the specialist burns unit at Broomfield Hospital, Chelmsford, in Essex.
They are both said to be in a critical condition.
She said the 17-year-old girl and a 20-year-old man from Hemel Hempstead suffered serious injuries.
She added: "At this stage we are unable to confirm the exact circumstances, but glass tubes and traces of accelerant (flammable substance) were found at the scene."
The final film in the Star Wars series, Revenge Of The Sith, arrived at UK cinemas last week.
One of the crucial scenes features a light sabre battle between Ewan McGregor's Obi-Wan Kenobi and Hayden Christensen as Anakin Skywalker.