A trade ministry official who was arrested last month on suspicion of attempting to smuggle a stimulant from the United States may have used drugs at his workplace, an investigative source said Thursday.

Several syringes were seized during a recent search of the desk used by Tetsuya Nishida, 28, deputy director of the Economy, Trade and Industry Ministry's automobile division, and police are now investigating whether he used stimulants at the office, the source said.

Police arrested the career-track bureaucrat on April 27 at his Tokyo home while he received a dummy package. The original parcel contained the illegal substance but it was intercepted and the contents replaced by investigators.

Nishida initially denied the allegation, saying he was not aware of the contents of the parcel, but later admitted that he had tried to obtain the stimulant for personal use, the source said.

The bureaucrat was quoted as saying that he had taken psychoactive drugs to deal with work-related stress, but began using stimulants "in search of more powerful effects," according to the source.

The suspect also said he smuggled stimulants purchased on websites based overseas for personal use and payments were made using bitcoin, the source said.

Police said the original package arrived in Japan on April 15. In it, they found 22 grams of a stimulant with a street value of about ¥1.3 million in a plastic bag that had been inserted inside a fashion magazine.

The package was addressed to another location but Nishida, who began working at the ministry in 2013, instructed the postal service to deliver it to his home instead, according to police.