A teacher was stabbed outside an adult education centre near Hamburg in northern Germany on Friday. A police spokesman told dpa that the 67-year-old man was critically injured in the attack. Two suspects were arrested on the grounds of the centre. They are two brothers in their early 20s, the police spokesman said. The background to the offence is still unclear, but it is being assumed that the victim and perpetrators knew each other. The police spokesman would not confirm or deny the possibility that the suspects were students at the centre. A police helicopter was used to support the manhunt…