The investigator previously testified finding rolled-up paper towels in the neck of the bottles.
Owen's attorney told jurors his client was imitating a movie actor when he threw the bottles into the street. Courbois said they did not contain an accelerant like kerosene or gasoline.
Owen has denied setting the deadly fire but told police detectives he did play around with two Molotov cocktails that broke on the street.
Detectives have said they do not believe Owen started the blaze by throwing a firebomb into the couple's home.
If convicted of murder, Owen could spend the rest of his life in prison.
If, however, he is acquitted on the murder charges and convicted of arson, Owen would be sentenced as a youthful offender and could be released from a juvenile treatment facility five months after turning 18.
Testimony in the trial begins Friday.