The headmaster of an exclusive London private school at the centre of a murder investigation after a pupil was “executed” in Brazil has said the “full story” is yet to come out.

Sergey Petrovich Danshin, 17, was shot three times in the back of the head after leaving a beachside villa near Rio de Janeiro that he was sharing with staff and other students from the £22,000-a-year International Community School, near Hyde Park.

The body of the teenager, who had allegedly gone out in search of drugs, was discovered on a canal bank the next day, less than 48 hours after the group arrived in the country.

Yesterday, headteacher Philip Hurd, 52, told the Standard: “There has been lots of speculation, but the school will give the full story. The full story will come out.”

Hurd, who is understood to have gone on the trip, was speaking from his home in Clapton, having just returned. 

Police believe Sergey, the son of a wealthy Russian businessman, was trying to buy cannabis and have described the crime as an “execution”.  Local police chief Julio Cesar Mulatinho Neto told the Mail on Sunday that the group had walked to a bar for pizza at about 6pm on September 27. He said the three adults left at about 11.30pm, leaving the four students alone in the venue.

“At about 1am, all four students returned and went to bed, but soon after two decided to leave the house in an attempt to buy cannabis,” he said.

“They returned to the bar but were not successful and returned to the house. Later, Sergey left alone. “He had only been in Brazil for two days. We do not understand the motive for this crime.”

Neto also revealed that Sergey’s backpack, containing an iPhone 5 and credit card, had been left untouched.

Renan Magalhaes Garcia Gutierrez, who owns the bar the group visited, claimed the under-age pupils downed vodka shots and smoked cigarettes.

He added: “When Sergey came back to the bar alone, he was asking where he could find cannabis and also made a sniffing gesture that I understood to mean cocaine.

“I told him ‘be careful - it’s dangerous here’. He laughed and said ‘don’t be silly, Brazil has no law’.”

It is understood Sergey’s father, Petr Danshin, an agricultural business magnate in the Black Sea city of Krasnodar, has flown to Brazil.

A school spokesman said: “We’re appalled by this tragedy and have done everything we can to help the Brazilian authorities with their investigations. We have offered our condolences to the family.”