Prosecutors in the YNW Melly double murder case could help prove their case against the rapper -- that is, if they can get their hands on his saliva and match it to DNA at the scene.
According to legal docs, obtained by TMZ, prosecutors are asking a Broward County judge to force Melly to submit an oral swab ... because they want to check if his C's, A's, G's and T's match up to DNA samples they found on a key piece of evidence collected during the investigation.
That evidence is a yellow jacket ... which prosecutors say already has DNA that matches Anthony Williams, one of the 2 people killed in the shooting.
Prosecutors claim there are 3 other potential DNA profiles on that jacket ... and seeing as how Melly is one of the people charged with the murders -- prosecutors wanna see if his DNA is also on the jacket.
As we reported, prosecutors allege Melly and his pal, Cortlen Henry, gunned down their buddies, Anthony Williams and Christopher Thomas Jr., and then hatched an elaborate plan to make it seem the men had died in a drive-by.