Can I be issued a traffic violation without a cop being witness to the incident?

This happened in Colorado!

Tl;dr My husband was issued a ticket for something that didn't happen and the ticket is solely based off of the word of a biker who broke a traffic law and a "witness" who didn't see the situation and is repeating what the biker told her to.

My husband (not myself) got a phone call from a Denver traffic cop this morning about an incident with a biker a week ago. My husbands side goes like this: he was at a 4 way intersection with a couple of cars on all sides. It was his right away after a few cars had gone and a biker coming from another way decided to jet through the stop sign without stopping, cutting off my husband which caused him to brake hard. My husband yelled "Not your turn" out the window and went on his way. The biker turned around in traffic and followed my husband, going as fast as he could until he got up to my husbands passenger window and started calling him names and yelling profanity. My husband then decided to pull over and talk with the biker about how what the biker did was illegal and that he instead should have stopped at the stop sign like everyone else on the road (HE NEVER GOT OUT OF HIS CAR AT ANY POINT IN THIS INTERACTION!). Things got heated and words were thrown around by both parties and my husband decided to drive off. As he did, he noticed a car behind him pull up next to the biker. This car was not around for 95% of the incident, including the failed stop sign.

Fast forward to today and my husband was called by the traffic officer. He said that he had a complaint and another person had also called in as a witness (no doubt the car that stopped at the biker after he drove off) and that he was going to issue my husband a ticket for reckless endangerment based off of the biker and witness saying that he had swerved at the biker (he says this is absolutely false, and I believe him 100% because he is level-headed and would NEVER do anything that could potentially harm anybody).

Is this legal? There was no cop present and nobody has any proof on either side of this situation. The witness was not present for most of the incident and obviously took the bikers side as soon as he stopped and talked to him-who knows what BS the biker made up?

I feel like we should fight this because my husband did nothing wrong and the biker obviously broke the law by going through the stop sign and was the initial person who acted crazy and started cussing etc.

Any advice would be awesome. We don't have any money to get a lawyer and this ticket is going to really set us back financially when I don't even believe my husband should be the one to receive the ticket.

(Also, this 4-way stop is at the end of the road and bikers frequently blow through it. It happens to me almost once a week and generally I'll give them a honk to let them know it wasn't their turn and they could have gotten somebody hurt!)