Arrange the following jumbled sentences and write the numbers in brackets.

(5) In fact, his luggage only contained textbooks and notebooks that he planned to take back home.

(2) However, at this moment, he received a notice from the US Immigration Service: He was not allowed to return to the country! He was forced to cancel his plane ticket.

(6) The persecution of Qian Xuesen by the US authorities aroused public indignation in the American scientific community, and many American friends came forward to rescue Qian Xuesen.

(1) In September 1950, Qian Xuesen completed the procedures for returning to China, bought a ticket to return to China, and handed his luggage to American Airlines.

(3) A few days later, Qian Xuesen was suddenly arrested and imprisoned in an island detention center, where he was tortured endlessly.

(4) The U.S. Customs opened his luggage for inspection and insisted that it contained important secrets and that Qian Xuesen was a spy.