The brother of a British man shot dead with his wife and mother-in-law in the French Alps is being questioned over the alleged fabrication of his late father's will, police said.

Zaid Hilli was arrested yesterday on suspicion of conspiracy to commit murder after officers uncovered evidence to suggest he doctored documents to ensure he inherited the estate, officials said.

Mr Hilli, 54, has previously denied any feud with his sibling over an inheritance.

Yesterday, detectives searched his home in Chessington, Surrey, and were later seen leaving the property with a plastic box, a ladder and two bags.

Eric Maillaud, Annecy's public prosecutor, said police would now try to find a link between the alleged fraud and the brutal attack which killed Saad and Ikbal Al Hilli, Mrs Al Hilli's mother Suhaila al Allaf, and local man Sylvain Mollier.

"We know there was a dispute between the two brothers over their father's will," he said.

"There are a certain number of documents that suggest Zaid attempted to fabricate his father's testimony in his favour.

"It looks like he tried to take the fortune for himself. That did not work but we want to ask him questions about it."

Mr Maillaud said detectives were aware of the allegedly false documents early on in the investigation.

The arrest is the first significant development in the inquiry after the attack on a remote mountain road close to lake Annecy on September 5.

Around 100 police officers in Britain and France have been tasked with investigating the killings.

French investigators have focused on three lines of inquiry: Mr al Hilli's work as an engineer, links to his native Iraq and his family.

Surrey Police yesterday said a 54-year-old suspect was arrested and detained.

Two children – Zainab, seven and Zeena, four, survived the attack and returned to the UK.