speeding evidence from a laser gun

Doesn't sound too optimistic, frankly.

Courts have a habit of believing police officers. Your only hope would be casting doubt on the reliability of the instrument or it's use by the officer concerned or in the circumstances.

You would need to know the type of instrument used, its techinical specifications, the instructions for use and the recommendations for settings, testing and maintenance, and to put the prosecution to proof that the specific instrument was working properly on the day.

You need to get hold of the manufacturer's instructions and technical specifications

Of course, the police will say that the instrument is tested regularly and in perfect working order but you would need to test this in cross-examination.

Was that particular instrument tested recently? By whom? How was it tested? Was this in accordance with the manufacturer's instructions? What is the evidence?

How old was the instrument? What is the history of defects and repairs?

If evidence is produced, is it documentary or oral?

Is there a note of the serial number of the instrument? Who did the test? Is that person available to be cross examined?

Most importantly -- will they they produce all the evidence at the hearing?

If they produce documentary evidence, who made the document? It might simply be hearsay and therefore inadmissible.

If the police officer giving evidence simply says that, yes, of course the instrument is regularly tested, was tested "only on the morning in question" and was in perfect working order, you need to ask him whether he, personally undertook these tests. If not, the court might be persuaded that his evidence is simply hearsay.

Where there is a "not guilty" plea to a speeding charge, the prosecution might assume that it is simply the motorist swearing "Speed? Me? Oh, no I didn't " with the police arguing: "oh, yes you did" and with the prosecution simply relying upon the verbal evidence of the officer concerned.

They might not be expecting a challenge to the reliability or use of the instrument itself

So, they might not have readily available the evidence to show that the relevant machine was properly tested , in working order and properly used.

You should call the police station and ask which instrument they use.

I would suggest that you do a Google search on the particular instrument and look for arguments which have been used elsewhere.

You need to get hold of the manufacturer's instructions and technical specifications

If you do decide to plead "not guilty", make sure the write out your questions beforehand re: testing, reliability, instructions for use and training of the officer concerned.

Also go back to the "scene of the crime" and think long and hard about any other cars in the area at the time -- is there anything to suggest that they might have "locked on" to the wrong car?

Where was the police officer positioned at the relevant time? How far away was he from your car? Was there a clear line of sight? What was the weather? Time of day? Lighting?

I do not practise law in Hong Kong but I understand that it is still based on English law which would mean that the burden of proof is on the prosecution -- they must prove their case beyond reasonable doubt. It is not for you to prove that you were not speeding --- it is them to prove that you were. That said, use of "speed guns" is pretty strong evidence against a driver.

It seems that your only hope is to cast some doubt on the instrument itself or its use -- it is highly unlikely that the court would accept that the police officer was lying so, unless you have strong evidence or suspicions to the contrary, I would certainly avoid making any such accusation.

What if you pleaded "not guilty" but are convicted? Well, you won't have any discount on the fine for a "guilty" plea and you will be ordered to make a contribution towards the prosecution costs. Don't ask me what those might be because I have no idea in Hong Kong.

Finally, you really should not rely on anything I say but take legal advice from a specialist criminal lawyer in Hong Kong. If, of course, you are prepared to pay for it

Good luck.

just being realistic. check to see if u have legal expenses insurance (for example, as part of your household insurance policy or AA (car club) membership)