It's a legal nightmare disposing of abandoned goods in Singapore because the the law is not currently clear on abandonment - I had to look into this some time back. There is not a clear definition of
property law for abandoned goods or what consists of abandonment (i.e. you cannot make an assumption that items have been abandoned) so you have to create it by writing a letter.
Cover your ass. Write a letter (registered post if possible) giving him one month to remove items or they will be considered to have been abandoned and will be disposed off. Keep a copy of the letter. If you make any money selling his stuff deduct only reasonable costs and remit the balance to him. You cannot charge for storage without a contract in place I believe. If there are obviously important documents (photos or diplomas) keep those for him or post to him. IF he makes a police report show them the letter as defence. If he complains stick to the date in the letter - "we gave you one month from the 5th Oct - the clock is ticking - come and get your shite deadbeat". He cannot reset the clock without your agreement.
The reason he has done this is that storage is expensive in Singapore.
Note: you can freely throw perishable or noxious items away now - you're covered there as they are a health hazard to you.
I not lawyer/teacher/CPA.
You've been arrested? Law Society of Singapore can provide referrals.
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http://www.ISS.edu
Your rugrat needs a School? Avoid for profit schools
You need Tax advice? Ask a CPA
You ran away without doing NS? Shame on you!