If someone wanted to write a mystery novel set in Southeast Asia, what might I suggest?
There are already too many tropes we've overused in fiction emerging from the region. So here are some tips to consider:
I'd avoid tourist murders and tourist murderers. It's overdone. There's plenty of Thai on Thai or Lao on Lao murders, thefts, scams and hustles in the big city and the villages that have taken place in real life or that can be written plausibly. A story shouldn't be interesting only because a falang was involved.
Avoid country mouse/city mouse stories and old world/new world East/West stories.
The supervisors and officials on the take is getting old. Which isn't to say it doesn't happen, but everyone's written about it. if you can't find a way to make it really interesting, leave it be.
Shamans, witch doctors, fortune tellers are colorful enough, but stop making them so integral to solving a case. This also applies to crimes during new years, major festivals, holidays or other special events.
If I wanted a cookbook, I'd get a cookbook. The same goes for primers on Buddhism and differences between East/West philosophy and politics.
And investigators really have to stop being the reincarnation of someone else important or significant to the plot, or using the supernatural to solve the crime. This isn't to say it's not a part of the culture, but it's really tiresome to see detectives who are doing no detecting, who would somehow be incapable of solving the crime except for divine intervention, coincidence or deus ex machina.
A Lao or Thai murder mystery can be a simple affair: Someone has gotten killed somewhere by someone who knows how to make it difficult to identify the killer's identity and motive. The outcome should usually be the victory of the investigator, using logic, reason and perhaps a little luck to identify, confront and apprehend the criminal and get back to doing whatever it is the investigator does at the beginning of the story.
This is a simplification but I think it's important to discuss the basics and encourage more Lao and Thai to write good mysteries and push ourselves to work that relies less on ornate and exotic trappings, excessive use of the supernatural and more on crime, law and the effort to bring order to their society.