The Las Vegas teen accused of fatally mowing down a retired police chief is now facing an attempted murder charge in a totally separate case … and prosecutors wanna lump this into his already-existing murder case.

18-year-old Jesus Ayala was charged for attempted murder earlier this month, with prosecutors in Nevada claiming he stabbed somebody in the Vegas area — which they say went down two months before he allegedly ran over Andreas Probst.

The authorities say the alleged victim told them Ayala and another person approached him on the street and started to use brass knuckles and knives on him — with the man claiming he sustained multiple lacerations to his torso as well as near his head.

Now, in light of this new info — the state wants to add the attempted murder charge to Ayala’s original case in a new indictment … according to new legal docs obtained by 360aproko.

Remember … in the OG case, prosecutors claimed Jesus was behind the wheel of a stolen car when he ran over a bicycliston the road back in August … killing the guy on the bike, who turned out to be retired police chief Andreas Probst. There was another teen in the car who is accused of recording the incident. Video of the alleged incident surfaced as well.

Like we said … prosecutors are now seeking to amend Ayala’s original charges to add the attempted murder charge from the stabbing incident — and their argument is … it’s related.

It’s not a done deal yet … Ayala’s legal team is pushing back against the amended charges — claiming the prosecution’s original case against their client is thin, which is why they’re trying to add something completely different in the 11th hour. A judge has yet to rule.