The unnamed suspect was taken into custody Tuesday in Clark County -- this according to the Las Vegas Metropolitan Police Department, which says they have their man. His identity has yet to be revealed ... he's also a minor -- just like his alleged accomplice.

The DAs said on Tuesday the 2 males are expected to be tried as adults, however. It was also revealed a student at a local school showed the shocking video to an officer on campus, which was how the department first learned of it.

Andreas Probst's daughter, Taylor, spoke about the loss of her father at the press conference ... saying her family is "devastated by the senseless murder" that took place last month, saying the death is a direct result of "society's decayed family values" and the effects of social media.

Remember, these two are who cops say is featured in a now notorious video that circulated online ... graphically depicting the murder of 64-year-old Probst, who was simply riding his bicycle down the street when the two guys in the stolen car opted to hit him.

You can hear them talking about it right before they hit the accelerator -- the guy driving asks his passenger if he should go for it ... and the passenger encourages him to do it.

Probst went flying into the air and was left for dead on the road. The two teenagers in the car can be heard laughing it up as they drive away.

Mind you ... right before they ran over Probst, the two had gotten into a separate road rage incident -- where they slammed into another car -- literally just moments beforehand.

However, authorities now say there was a third incident that went down roughly 30 minutes before all of this ... where the 2 teens hit another person on a bike, claiming the passenger was the one behind the wheel this time.

They say the other cyclist and the alleged road rage victim suffered non-life-threatening injuries.

The video has drawn widespread outrage and condemnation ... and Vegas PD has since publicly pleaded for help in ID'ing the other dude. Now, police say they have them both.