Sadism, revenge, hate, boredom, greed. These can all be motives for the crime of arson, experts say.

A string of recent fires in Easton, Middleboro, Hanson and Plympton have been declared intentionally set or deemed suspicious, although authorities have not said whether the fires are connected. The string of blazes is still under investigation, officials said Wednesday.

Jack Levin, a professor of sociology and criminology at Northeastern University, said there are some common threads to arson, despite the crime’s complexities.