Alexander Raymond Iacuone, 23, Alexander Duffy, 24, and another man, who cannot be named as he was under 18 at the time, were last year found guilty in the ACT Supreme Court of conspiracy to murder and sentenced to varying jail terms.

But Canberra prosecutors said the amount of time the offenders will spend behind bars was too short and did not reflect the seriousness of the crime.

The office of the ACT director of public prosecutions appealed the sentences as manifestly inadequate and on Wednesday urged the ACT Court of Appeal to increase the amount of time to be served.

Lawyers for the trio argued against a sentence increase, saying the punishment had been within range.

In 2008, the trio conspired to use a baseball bat to murder the victim. They lured the 17-year-old victim from his Tuggeranong home and chased him into bushland.

Duffy found the victim and helped him avoid the others and then left the area.

But Iacuone and the juvenile caught the victim soon after. The pair forced him onto his knees, with his hands on his head, and then told him he would be killed and his body buried at the Cotter.

Iacuone choked him and the pair fell to ground, while the juvenile hit the victim with the baseball bat.

The teen escaped to safety after they fell into a nearby creek during the scuffle.

Iacuone and the juvenile were arrested in a car near the victim's home.

Iacuone was sentenced to five years' jail, to be served in full-time custody for 18 months, followed by 12 months' weekend detention, and then suspended for the remaining two years and six months.

Iacuone was also ordered to enter a three-and-a-half-year good behaviour order.

The juvenile, who is now 22, was sentenced to four years' jail, with one year in full time custody, nine months in periodic detention, and the rest suspended on condition of a three-year good behaviour order.

Duffy was sentenced to two years and nine months' jail, to be served by way of 18 months periodic detention, with the rest of the sentence to be suspended.

Director of Public Prosecutions Jon White, described the crime as a “cold blooded, calculated plot” which only failed because of the conspirators' own incompetence.

Mr White said the punishment meted out by the court had been manifestly inadequate and “so low as to shock the public conscience”.

He also said the structure of the sentence had been wrong, with the offenders ordered to serve insufficient time behind bars.

But lawyers for the trio, Hament Dhanji SC and Ken Archer, argued their clients had the “physical opportunity” to kill the victim, but did not.

Mr Dhanji said the sentences had been within the range of the sentencing judge’s discretion.

The three appeal judges - Chief Justice Helen Murrell, Justice Richard Refshauge, and Justice Iain Ross – reserved their decision.