I refer to the tragedy in Corfu where two young children died through carbon manoxide poisoning.

From the BBC website I have copied the following:

"Chief of police Dimitris Bineris said the hotel owner, hotel manager, maintenance manager and an engineer who installed an air conditioning unit would be charged with negligent manslaughter once toxicology tests on the children's blood have been completed."
My question is: why is the air conditioning engineer being held?
Maybe in Greece the sc systems are linked with the gas