Arson conviction record defended by Devon and Cornwall Police
Figures showing the number of people convicted of arson have been defended by Devon and Cornwall Police.
A Freedom of Information request by BBC News showed 61 people were convicted of arson in Cornwall between 2009-2011, when 684 offences were recorded.
Insp Mark Bolt said many crimes were minor and some people had been convicted for many attacks.
He added that there was often "no viable lines of enquiry" and there were no witnesses to many of the attacks.
Insp Bolt said: "Arson is criminal damage with fire, so it's any damage that gets reported where there is a fire element, so it will include cigarette burns and electrical fires that we don't know the cause of.
"There are very, very few serious reports of arson and the figures are full of these little minor incidents which are incredibly difficult to detect."
Pengarth Day Centre in Penzance, which looks after about 160 people each week, was targeted by arsonists in December 2011 and had to close for a week.
Centre manager Sharon Mitchell said: "A lot of people had to stay at home that week, some of them didn't see a person the whole week we were closed."
A police spokesperson said no-one had been convicted of the fire which was started in a wheelie bin next to the centre.
Insp Bolt said: "There's often no viable lines of enquiry to follow because there are no witnesses... it happens instantly and there's very little forensic evidence.
Ms Mitchell said it was "frustrating" that no-one had been convicted, although she understood the problems.