The Supreme Court upheld the death sentence passed by the two lower courts on the three defendants the headlining murder of a restaurant waitress in 2016.
The court's ruling was read out at Talingchan Criminal Court on Tuesday.
Facing the death sentence are former Lt Chaiyut Benjachart, 44, former Pol Sen Sgt Maj Samat Saengsin, 51, and former Pol Sgt Maj 1st Class Phanumet Meela.
Prosecutors previously told the courts that the three defendants were hired by former Pol Col Amnuay Pongsawat, then superintendent of Ban Pong police station in Ratchaburi province, and Sanong Somsit to abduct Supaksorn "Ying" Polthaisong, a restaurant waitress. The woman was said to be a tomboy and to have become romantically involved with a songstress that Pol Col Amnuay had been dating.
On Dec 13, 2016, the three abducted Supaksorn, who was 28 at the time, in the Buddha Monthon 4 area near Bangkok, took her away in a pickup and detained her at various places in Kanchanaburi.
The three later killed Supakorn by suffocating her, took her body to a resort in Kanchanaburi and buried her there.
The court of first instance found them guilty and sentenced all three to death. The Appeal Court upheld the death sentence. They took the case to the Supreme Court.
The death sentence was, again, upheld by the Supreme Court.
A separate case was brought against Amnuay and Sanong and three other people - Niwat Saithong, Phumithat Piboonsawat and Kannika Krumram - for conspiring in the murder of Supaksorn.
On July 31, 2019, the court of first instance sentenced Niwat and Phumithat to death. The sentence was commuted to life. Amnuay was given 15 years and Sanong 10 years in prison.
The other defendant, Ms Kannika, was acquitted.