She was, however, let go after a high flying individual called senior KAA officials to secure her release.
The incident has been handled with the strictest confidentiality, with no official records showing Monica was at the airport on the material day.
Undercover police officers at JKIA, who requested anonymity, told the Star how Monica was briefly detained by customs and immigration officers but the incident didn’t bear much significance until later when they identified her as the same woman who was brutally murdered.
The police officers have curiously been following the news of the murder and subsequent investigation in the media.
But Kenya Airport Authority Communication Manager Angela Tilitei distanced the institution from the incident.
"KAA does not have the mandate to detain any passengers. It is either immigration, port health or Kenya Airports Police Unit," she told the Star.
Immigration Principal Secretary Gordon Kihalangwa also said the matter never came to his attention adding that his officers only deal with passport matters.
"One thing I am sure of is that Monica never had a diplomatic passport as had been claimed. She bore the ordinary one,” he said.
"Secondly, with regard to whether she was detained for failing to declare the money she had, am not aware because that is the docket of the customs department," Kihalangwa told the Star.
He however noted that if one is detained for more than an hour at the airport, an official report is supposed to be recorded.
There is no official record of her detention despite sources telling the Star that she was indeed held for about four hours at the airport.
It is claimed that a red flag was raised after it emerged that she was carrying more money, in foreign currency, than she had declared.
Investigators have told the court, where they have arraigned two suspects, that they are still investigating the possibility of money having been stolen from Monica in her killing.
"The investigations are ongoing to establish any money that could have been taken from the deceased’s house. The deceased was to travel out of the country," an affidavit by investigating officer Maxwell Otieno reads.
He said they are tracing the money movement, persons involved, and how and who is currently in possession of the money.
The prosecution hinted that its investigations will go beyond Kenyan territory but did not elaborate.
Monica lived flamboyantly going by her social media accounts where she more than once this year posted photos of big amounts of money.
Efforts to reach her family to confirm whether Monica was transporting any money or if they had received the money she allegedly had proved futile.
Monica's body was found inside a bathtub on September 21 by her brother who told police they had to break into the house after knocking several times. She was scheduled to fly to Dubai the same evening.
Both her feet and hands tied behind her back, an indication that she was tortured, according to the police.
Her throat had been slit, ear to ear and her mouth was taped shut, which police say are hallmarks of a professional killer.
According to the relatives, Monica had just returned to the country on September 19 from South Sudan where she worked.