Who murdered the English Teacher?

It's the beginning of a new academic year, and the English teacher has been murdered. There are three suspects; The maths teacher, who was taking a mid-year test. The gardener, who was outside, cutting the hedges. The headteacher, who was in a meeting. The maths teacher who was in her class, a couple of doors away from the English teacher, while she was taking the mid-year test. The gardener was the closest, as he was outside the class while he was cutting the hedges. However, the blinds were drawn. The headteacher, was the furthest as he was in a meeting in his office, on the other side of the school. Which one committed the murder?