SINGAPORE - Intrigued by the workings of a Nerf gun, a plastic toy that fires foam projectiles, a 64-year-old sheet-metal worker manufactured several metal airguns capable of launching 6mm steel ball bearings.

To test the range of his airgun, Lee Keng Hee shot the bearings from his Jurong West home, initially at trees.

After building a more powerful third gun, Lee targeted the neighbouring blocks, breaking the windows of some units.

On Wednesday (Dec 16), Lee was sentenced to 18 weeks' jail and a fine of $2,000 for manufacturing an arm without a licence and shooting the metal ball bearings at the residential blocks.

Two other related charges were taken into consideration for his sentencing.

Deputy Public Prosecutor Regina Lim described the airgun Lee manufactured and shot at flats as inherently dangerous.

She said the ball bearings were able to crack glass over 77m away and Lee had "a high degree of persistence", spending 10 months manufacturing several guns.

The DPP noted that Lee shot more than 200 ball bearings using his airguns.

Lee's lawyer, Mr Favian Kang, argued that his client is remorseful and had "made restitution voluntarily (and was) not prompted".

He added that Lee sold his late mother's jewellery to make restitution.

The court heard that Lee had come across a Nerf gun in 2017 and began studying its mechanism.

He decided to make an airgun from scratch by watching videos on YouTube and collecting scrap metal from his workplace.

While completing his first two airguns in 2018, Lee bought 100 6mm steel ball bearings and 100 8mm steel ball bearings to test them out in his home.

In October 2018, he completed a third more powerful airgun.

According to court documents, Lee wanted it to have better power and consistency compared to the first two.

He constructed it with a bigger air chamber, so that he could fire more ball bearings with each full pump of the air chamber.

Lee shot at trees and the neighbouring Housing Board blocks outside his eighth-floor flat, usually out of sight of his wife and son who live with him.

From these tests, he was satisfied that the third airgun was able to consistently fire the 6mm ball bearings into the concrete walls of Block 453 Jurong West Street 42, which is across from where he lives.

He continued using the block for target practice until April 2019.

On April 3, 2019, a resident called the police at about 8pm, saying that he heard a crack before discovering his bedroom window was broken.

Lee was eventually arrested after the police found an airgun in his home.

Flats that suffered damage were in the line of sight of Lee's flat.

Tests run by the authorities found that the ball bearings shot from the airgun had enough power to cause non-lethal injuries if aimed at a person.

The speed of the ball bearing upon impact was found to be fast enough to crack the glass of a window.

For manufacturing or dealing guns, an offender can be jailed up to three years and fined up to $10,000.

For committing a rash act, an offender can face a jail term of up to six months or a fine of up to $2,500, or both.