I plan to apply for a Retirement Visa in Los Angles in March. I understand there is a background investigation report needed. What agency FBI, Local Police, State Police? Any help is appreciated.

Assuming you are a US citizen, there is an easier way which avoids the need for a background check and a medical certificate.

Enter on a tourist visa, file an application to convert that to a Non immigrant visa, then apply to extend that on an annual basis. Financial requirements/90 day reporting all remain the same, with the exception of the fact that if you are relying on bank deposit for all or part of the qualifying funds, they must be lodged in a bank in Thailand, not the US.

They don't specify what agency has to do it. You can go to your local police to request it. Many states now have an agency that does them and you can request it online and the finger printing is done electronically at designatde locations.

Assuming you are a US citizen, there is an easier way which avoids the need for a background check and a medical certificate.

Enter on a tourist visa, file an application to convert that to a Non immigrant visa, then apply to extend that on an annual basis. Financial requirements/90 day reporting all remain the same, with the exception of the fact that if you are relying on bank deposit for all or part of the qualifying funds, they must be lodged in a bank in Thailand, not the US.

That is not as easy to do as it was before unless you live in Bangkok. They have taken away the ability to do the conversions from the local offices. For many now it means 2 trips to Bangkok immigration to get it done.

The best alternative is to get a single entry non-o visa from one of the honorary consulates.

I went to LAPD to get my background check (about 10 years ago). LAPD has an office down at HQ that does this. I waited just a few minutes for their check to be done. Note: about 12 years before this, I'd had a drunk driving conviction. The sergeant came over to me and asked if the DUI might affect my visa application and I told her I didn't know if it would. She then said 'Here's what I will do. I'll write the background check to say you had never been arrested or convicted of a felony.' She was very accommodating and helpful.

Assuming you are a US citizen, there is an easier way which avoids the need for a background check and a medical certificate.

Enter on a tourist visa, file an application to convert that to a Non immigrant visa, then apply to extend that on an annual basis. Financial requirements/90 day reporting all remain the same, with the exception of the fact that if you are relying on bank deposit for all or part of the qualifying funds, they must be lodged in a bank in Thailand, not the US.

I found the process to get an O-A easy and I avoided all the hassle associated with starting with a tourist visa that one would face these days. You get nearly two years without the need to apply for an extension or meet financial requirements. I'm American but got it in another country. The Thai consulate there was fine with a local police report.

Alternatively, as UbonJoe said, starting with a non-imm O would at least mean skipping the hassle of getting a conversion to a non-imm O entry from a tourist visa entry.

Of course LA consulate won't give a single entry O based on a retirement reason.