Your number one point is probably the only scenario where the killing of the older Mr Tan could be justified, i.e. self defence. No other circumstance is justified.
Regarding your second point, why would the younger Tan be trapped underneath the car?
It still appears that the suspect was the aggressor. There is even less doubt that he "started it", what with his indebtedness, his failure to declare, his sensing an opportunity when the elder Mr Tan went to his station to make the report.
yes, why would the younger Tan be trapped under the car?
my thinking is when the policeman reverse, he hit the younger Tan and when he fell down, the policeman drove over him, thus tangling Tan's body underneath the car body.
3. my thinking of this case is that, the money owe by the policeman does not belong to his debts. in another words, it may be that the policeman is taking on some loans on behalf of the elder Tan. (i might be wrong, but think in a logical way) example. if u are going to be bankrupt due to ur own gambling debts, and u only have 1 rich friend who has the money. u approach him for money. he rejected u. do u kill him, or move on?
we now change the scenario a bit. if u are going to be bankrupt because u help a friend to take some loans for him to tide over his business. then ur friend finances recovered, but still have not service the loan that u took for him. he rejected u ( as in play u out, by saying lame excuses as 'loan is u take, because under ur own name') i think most people will probably scold or bash him, but this is the normal reaction.
however, if we were to follow my argument, how come is the elder Tan start to attack the policeman first? (mentioned in point 1) there must be some pawns that the policeman knew, and it was detrimental to the elder Tan. might be some dirty secrets that elder Tan might be harbouring. when the policeman threaten elder Tan that if he fails to provide financial help, he will tell the whole world his dirty secret. this enrages Tan and causes him to trip and attack the policeman.
4. before elder Tan went home, it was said that he went to cisco to take out some documents from safe box. then meet with policeman at home. elder Tan died. policeman next day declared bankrupt. see the linkage? documents, next day bankrupt. this shows that the policeman is at his wits end. whether or not he has the intention to murder, it must have something to do with elder Tan. you dont go around killing ramdom people when u are about to be bankrupt. you will normally bring the person that causes u to bankrupt DOWM with u.
all this is based on my own judgement of this case. please do not say i am siding who. i do not know both of them but i just took an interest in this case.