But the defence counsel said his client was innocent and that the confession was secured “under duress”.
"We call on you, in the name of society, to return safety and security to this society by hitting hard against everyone who considers threatening it," chief prosecutor Hussein al-Huraiti said in his closing statement.
He urged the court to hand down the "maximum penalty", without specifying the sentence terms, against 25-year-old Sami al-Mutairi when it issues its verdict on 4 June. Murder is punishable by death in Kuwait.
"I know that in this case, there is no evidence that proves beyond doubt that Sami al-Mutairi was the one who committed it. And this is why the confession was important," the attorney said, complaining his client had been "tortured" by state security on more than one occasion.
Mutairi is accused of carrying out a highway ambush in January that killed Michael Rene Pouliot and seriously wounded David Caraway, both contractors for the US army.
Second fatal attack
Two other Kuwaitis, Badi Cruz al-Ajmi and Khalifa Hilal al-Dihani are also on trial for selling Mutairi the Kalashnikov assault rifle and ammunition used in the attack.
The shooting, carried out near Camp Doha, the largest US army base in Kuwait, was the second fatal attack against US personnel in the emirate since last October and the first to target civilians.
Mutairi shot the two men and then went to a mosque to pray before he headed for his office where he heard on satellite television that his attack was a success, the prosecution added.
The defence has maintained throughout the trial that all three defendants confessed under duress.
Last month, the court was shown a confession tape in which Mutairi, who has pleaded not guilty to the shooting, said he did not regret the attack and would do it again if freed.
The two other defendants have also pleaded not guilty to arms possession and sale, and claimed they never knew Mutairi before the trial opened in February.