DENVER (CBS4)– Police in Denver hope two new billboards and 20 bus stop ads will bring in tips to help them track down a hit and run driver that killed two boys.

Police have released surveillance video showing a large white or silver SUV speeding away from the scene at 14th and Yosemite but it hasn’t gotten them very far in making an arrest.

In March, Ah Zet Khan, 6, and his brother Za May Khan, 8, were struck and killed at the corner of 14th and Yosemite.

They were crossing the street with their mother, Zamar Bee. She survived but has critical injuries.

The message on the billboard reads, “Someone knows who killed our sons” and urges people with information to pick up the phone and call police.

Tears streamed down Bee’s face at the unveiling of the billboard as she pleaded with the driver to come forward.

“Please come forward and take responsibility,” said Bee through an interpreter. “She wants him to understand that she loves her two sons and wants him to come forward.”

Bee and her sons fled Myanmar as refugees and were searching for a better life in Colorado when they were struck.

The reward for information leading to an arrest of the driver has increased thanks to an anonymous $1,000 donation from a CBS4 viewer. The reward now totals $21,000.

“We hope the money motivates you, yes, but we hope we can tap into your sense of being and allow you to make the call,” said Crime Stoppers Vice President Larry Stevenson.

Police said they have officers, limousine, cab and truck drivers all over Colorado looking for the driver that killed the young brothers.

“We are looking for a ghost right now but family members, you know something. The person that possibly repaired the car, you know something. The person that possibly bought the car, you may know something,” said Stevenson.

Police said even a small tip could make a big difference.

A $20,000 fund has also been established for Zamar from public donations that is intended to help with her injuries.

Anyone with information regarding the hit and run is asked to contact Crime Stoppers at 720-913-STOP (7867). You can text to CRIMES (274637) then title DMCS and enter your message or send an e-mail to If the information you provide leads to the arrest and charging of a wanted individual, you can receive a cash reward up to $2,000.