A police corporal who threatened to send a man's teenage cousin to a girl's home unless he paid him a $150 "fine" was jailed for five months on Wednesday.

Shawn Lim Zi Han, 22, an investigation officer with Clementi Neighbourhood Police Centre (NPC), admitted cheating the 33-year-old man who had gone to him after his 14-year-old relative was reported for stealing a wallet.

A district court heard that Lim had recommended that the girl be placed on a guidance programme over the incident at City Vibe mall in August 2012.

Investigations found that Lim asked the girl's mother to pay him a fine of $150, after which the case would be closed.

The mother subsequently called her daughter's 33-year-old cousin to accompany her to the NPC on Aug 20. There, Lim told him to pay the $150 otherwise his cousin could be sent to a girls' home.

Believing it was a legitimate procedure, the cousin gave Lim $150 and thought the case would be settled.

However the case was reassigned to another investigation officer, Ms Noraini Hussain, 32, who told the teen and her parents to attend a guidance programme introductory meeting. The mother told her that they had paid $150 to Lim who gave the assurance that the case would be closed.

When Ms Noraini checked with Lim, he said the payment was a "settlement".

But the teenager's mother maintained that the cash was a "fine" and not compensation. The officer then found that the acknowledgement slip was not in the investigation paper and lodged a police report against Lim on Dec 27 that year for cheating.

Another similar charge involving $150 was taken into consideration. Lim, who has made full restitution of $300, could have been jailed for up to 10 years and fined.