A 22-year-old Sikh software engineering student has been stabbed to death in his taxi allegedly by an American student who was upset over not getting admission into a university, media reports said. Gagandeep Singh, a third year student who was also working as a taxi driver, was allegedly attacked by the 19- year-old passenger he had picked up at Spokane International Airport in Washington State on August 28, NBC affiliate KHQ reported.