Christianne Shepherd, seven, and her six-year-old brother Robert, from Wakefield, West Yorkshire, died after a faulty boiler leaked gas into their Corfu bungalow in October 2006.
The children were on half-term holiday with their father, Neil Shepherd, and his partner, Ruth Beatson, who were both left in a coma as a result of the accident but survived.
Thomas Cook employees Richard Carson, 28, and Nicola Gibson, 26, are charged, along with nine Greeks, with manslaughter by negligence in relation to the children and causing bodily injury by negligence to Mr Shepherd and Ms Beatson.
They face up to five years in prison if found guilty.
The court heard that, as a consumer affairs executive, Carson, a "relatively junior employee", was expected to visit hotels and fill in a health and safety questionnaire.
Carson has been criticised for accepting the word of the manager at the Louis Corcyra Beach Hotel, in Gouvia, that no gas was being used to heat water in the bungalows.
During the trial, Corfu Town courthouse heard that carbon monoxide fumes leaked into the family bungalow from an outhouse next door.
But Illias Anagnostopoulos, defending Carson, told the court today that his client was a "diligent" and "honourable" young man who had carried out his duties.
He said: "He fulfilled his requirements and did what was reasonably expected of him to do.
"He was not responsible for safety. He was not a security official. He was not a private detective.
"Whoever says that Mr Carson should have been like a detective investigating a crime scene?"
He said that, in the course of his work, he should have been able to expect answers in "good faith and honour" and not that he was dealing with "criminals, crooks and no-goods".
He said Carson should also have been able to expect that, in a European country like Greece, the installation of boilers was carried out according to domestic legislation.
He said: "All these things are without the scope of responsibility of the Thomas Cook employee, these are within the scope of responsibility of the Greek state."
Mr Anagnostopoulos said Thomas Cook employees carried out hotel inspections under a voluntary code of conduct and should not be punished "because they strive for better qualities rendered to their clients".
He accused the other defendants of playing a game of legal "table tennis" as they strove to blame each other.
The court has heard that Carson, who took a three-year course in tourism enterprise, had little knowledge of gas.
The prosecutors argued that a thorough audit of the bungalows would have shown it was being used in the rooms.
Mr Anagnostopoulos said Carson's questionnaire, which identified the need for a phone in the children's club and the illumination of steps leading to the swimming pool, proved he was a diligent employee.
The court heard that the boiler in question was in a "repulsive" state and was "decrepit" with "rust corrosion".
Not only was there no chimney for the boiler, the thermostatic safety valve had been bypassed.
Mr Anagnostopoulos said the "immoral behaviour" which allowed this to happen was to blame for the children's deaths.
The court heard that Gibson was a holiday representative whose duties included greeting and looking after clients.
She also had the responsibility of walking around the hotel once a month to check if anything was wrong and fill in a form.
Grigoris Damaras, defending, said she could not be expected to have known gas boilers were being used to heat the water in the rooms.
He said: "She wanders around the place where tourists live and breathe every day. This is what she was trained to do regardless of how long her training lasted.
"This is what they told her to do. This is what she did. There's absolutely nothing to indicate that what she had to do she did in a faulty way."
He said it was "unfair" to target Gibson who was the "last link" in the chain of responsibility, adding: "When we include people in the chain as links we must explain why this is so."
The court has heard that hotel manager Georgios Chrysikopoulos, Petros Stoyiannos, the head of the technical department at the hotel, and Christos Louvros, a hotel electrician, all failed to act despite the poor state of the boiler.
Boiler maintenance engineers Theo Koromios and Nikolaos Varthis warned the hotel not to bypass the thermostats.
But they were blamed for not doing more to ensure the safety of the devices which they knew were operating without chimneys.
Prosecutors blamed architect Alexandros Gavrielidis and civil engineer Dimitrios Xidias for designing and building the outhouses without an outlet.
Also on trial are safety technician Damianis Goudelis, who signed the safety certificates for the hotel, and Michael Florentiadis, who renovated the roof in 2001.
He replaced the corrugated iron roof with a tile roof which sealed the outhouse and therefore trapped the fumes.
Stoyiannos, Xidias, Gavrielidis and Florentiadis are also accused of breaching building regulations.
The panel of three judges retired to consider their verdict.
