Police say they have an open mind on who made the bombs found in Freeland, despite claims the devices were the work of a British Unabomber, writes Emma Henry.

The sophisticated nature of the cache found at Eynsham Park just over a week ago has led to speculation they were the work of a bomber never encountered before.

Comparisons were made with American Ted Kaczynski. Known as the Unabomber, he terrorised the USA with an apparently random bombing campaign lasting 18 years until he was jailed for life after being turned in by his brother. But Acting Supt Euan Read, who is leading the Thames Valley Police investigation, said it was too early to say if the would-be bomber was a loner or part of an organised group.

What was clear, he said, was the bombs were put together by someone with an extensive knowledge of electronics and a lot of patience. The maker may have gained his expertise from military training. Acting Supt Read said: "They were extremely sophisticated, there is no doubt about it. These would have taken time to build. They were cleverly constructed and cleverly designed and it would need more than just a quick squint at the Internet to build one.

"These must have taken weeks of determined, focused expertise to make. We are thankful they did not explode.

They were designed to shred everything around them. "The man who built these is clearly a perfectionist and is certainly very intelligent. But as far as who it is, a group or a lone individual, either is possible. We are still open-minded."

He said officers had not ruled out a link to established terrorist groups.

The incident room at Cowley police station has received hundreds of calls and a team of 25 detectives are following up a number of leads. Officers are working closely with police in Gloucestershire, where a similar bomb was found a week earlier, and Scotland Yard's anti-terrorist branch.