SINGAPORE - A 42-year-old man was sentenced to 15 months' jail on Friday (Sept 8) for tying up and assaulting a boy whom he suspected of hacking into his mobile phone.

The court heard that Muhamad Zaidi Saleh had amphetamine use disorder and tested "presumptively positive" for the drug in an internal test by the Institute of Mental Health.

However, court documents did not mention if he had consumed narcotics shortly before committing the offences.

He pleaded guilty to assaulting the 14-year-old stranger when he tried to obtain a confession from him.

One count of wrongfully confining the teenager in his Tampines flat for almost two hours on Nov 18 last year was taken into consideration during sentencing.

Zaidi was trying to unlock his Google account outside his flat that day when paranoia set in, leading him to assume that somebody had hacked into it.

His mobile phone then received five messages while he was fiddling with it.

Zaidi suddenly heard a message notification tone coming from a nearby staircase and spotted the boy at the void deck.

He immediately concluded that the sound came from the teenager's phone and believed the simultaneous receipt of messages could not have been a mere coincidence.

Suspecting the boy to be a hacker, Zaidi confronted him downstairs around 12.15am.

Deputy Public Prosecutor Joshua Rene Jeyaraj said the teenager was high on methamphetamine, or Ice, at that time.

Zaidi, who did not identify himself, asked the boy to hand over his mobile phone, and the boy did as he was told.

It was likely that the boy was in a state of intoxication and was not thinking straight, the court heard.

Zaidi then threatened to call the police and asked the teenager to follow him to his flat.

DPP Joshua said: "The victim, shocked that the accused had somehow guessed that he had consumed drugs, and worried that the accused might be a police officer, obliged."

Zaidi then secured his front gate with a padlock and locked the main door after the boy handed over his wallet.

He started to interrogate the boy, who denied hacking into the man's phone. Zaidi kept repeating the same questions for about an hour and grew increasingly dissatisfied when the boy kept on giving him the same answers.

At around 1.40am, he got some rope and tied the boy's wrists behind his back while the youngster sat in a chair. Zaidi also secured the teenager's legs to the legs of the chair and continued interrogating his victim, who did not resist.

"The accused only got more frustrated and would assault the victim whenever his answers were unsatisfactory. In total, the accused slapped both sides of the victim's face several times, punched the victim once in his left eye, once in his right cheek and once on the top of his head," said DPP Joshua.

The commotion roused Zaidi's family members from their sleep, and one of them called the police at around 2.10am.

Zaidi finally freed the boy and allowed him to leave the unit. Officers soon arrived at the scene to arrest Zaidi.

Court documents did not state if the authorities dealt with the boy afterwards for drug abuse.

The teenager and his parents went to Chang General Hospital later that day. He was found to be suffering from multiple bruises, and was given outpatient leave from Nov 18 to Dec 1 last year.

Zaidi is now out on bail of $15,000 and will surrender himself to the State Courts to begin his sentence on Sept 22.

For assaulting the boy while trying to obtain a confession, he could have been jailed for up to seven years and fined or caned.