premise: Turkish security forces impounded 80 kg of heroin in an operation in eastern Turkey on Friday, the semi-official Anatolia news agency reported.
  Acting on a tip-off, security forces stopped and searched a lorry in Muradiye town of Van province, said the report.
  With the help of a sniffer dog, police found 160 packages of heroin stashed in secret parts of the truck, the report said, adding that the driver of the lorry was taken into custody on charges of illicit drug trafficking.
  Turkey is on a key transit route for gangs smuggling drugs from Asia and the Middle East to markets in western Europe.
  
  In 2005, Turkish security forces seized 6,663 kg of heroin, 140 kg of morphine, 34 kg of opium, 6,002 kg of hashish, 40 kg of cocaine, some 1.23 million captagon pills and 5.76 million ecstasy pills, according to official figures.
   What event caused the security forces to stop and search a lorry in Muradiye?
hypothesis: Acting on a tip-off