Three other accomplices, including the two teenage girls, were also convicted for the crime, which took place in Solna in September 2013.
The 32-year-old victim had been beaten and stabbed to death and robbed of 5,000 kronor ($760). Police found his body in a wooded area in the Frösunda district of Solna, north of Stockholm.
The victim had come to the scene following an online exchange with the girls during which they promised to have sex with him in exchange for money.
"We get turned on by doing it outside," one of the girls wrote in a text message hours before the killing, the Aftonbladet newspaper reported.
The girls, aged 16 and 18, then met up with the man at a petrol station and asked him to withdraw cash from a teller machine.
In its ruling, the court stated that the girls had supported themselves by tricking unwitting male victims contacted on dating websites.
"They set up dates with men who wanted to buy sex from them, took payment in advance, and then found excuses to leave the men without fulfilling the sex purchase," the Solna District Court wrote in its decision.
After the 32-year-old withdrew cash, he walked with the teens to a nearby wooded area where the three male accomplices were waiting.
Two of the men, aged 25 and 26, faced charges of murder, while the girls and a 29-year-old man were charged with aggravated robbery, with an alternative charge of accessory to aggravated robbery.
Despite the 26-year-old's claims of innocence, the court believed there was sufficient evidence to prove he delivered the 18 stab wounds that killed the 32-year-old.
His 25-year-old accomplice was acquitted of murder, but convicted of aggravated robbery, receiving a five-and-a-half-year prison sentence.
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The teenage girls were convicted for aggravated robbery and each sentenced to 18 months of juvenile detention.
However the 29-year-old was acquitted of being an accessory to robbery.
The court also ordered the 26-year-old to pay 118,059 kronor in compensation to the victim's family.