Speaking with Khaosod newspaper, the Saudi embassy's first secretary, Abdulsalam Abdullah R Alenazi, said the decision to recall charge d'affaires Abdalelah Alsheaiby came directly from King Abdullah on July 18.
The recall was made in line with a recommendation made by a Saudi panel monitoring the case, Mr Alenazi said.
According to the first secretary, Mr Alsheaiby is now in the process of advising the Saudi government on the al-Ruwaili case.
The timing of his return to Thailand would depend on the actions taken by Thai authorities, he said.
Mr Alsheaiby was recalled five days before Gen Somjate Boonthanom, a former senator and brother of Pol Lt Gen Somkid Boonthanom, a defendant in the murder case, was appointed to the National Legislative Assembly at the end of last month.
Al-Ruwaili went missing in Bangkok on Feb 12, 1990, and is presumed dead.
Pol Lt Gen Somkid was one of five former police officers accused of the kidnapping and murder. The others are Pol Col Sorarak Jusanit, Pol Col Praphas Piyamongkol, Pol Lt Col Suradej Udomdee and Pol Sgt Maj Prasong Thongrung.
The Criminal Court acquitted the five defendants on March 21.
When prosecutors lodged an appeal against the acquittal shortly before the June 30 deadline, they raised three points of contention.
These were the Criminal Court’s rebuttal of a key witness; the rejection of a ring presented as evidence implicating the defendants; and the abrupt change of the presiding judge before the court’s ruling.
The court had said there was insufficient evidence to prove the defendants were guilty.