Ever Valles, 19, is accused of murdering Timothy Cruz, 32, on February 7 after robbing him at a light railway station in the early hours of the morning.
The teenager had been freed by the Denver Sheriff's Department in late December after posting $5,000 bond for theft charges.
They let him go despite requests from US Immigration and Customs Enforcement agents to keep the gangster behind bars so that they could deport him.
They flagged him as an 'immigration priority' given his ties to gang activity in the city and asked to be told by the jail when it planned to release him so that they could be there waiting to take him into federal custody.
On December 20 however, a fax notifying ICE that Valles was due to be released was only sent 30 minutes before he was back on the streets.
No one at ICE saw it in time to get to the county jail to collect him, The Denver Post reports.
Valles now faces first-degree robbery and murder charges along with Nathan Valdez, a 19-year-old US citizen who is also accused of killing Cruz.
He was arrested on February 8 after an anonymous tip led police to him.
On the day of the killing, officers shared surveillance footage of two masked suspects they believed shot Cruz.
…Valles is a known gang member whose gang history is documented in the Colorado gang database.'
Denver is considered a 'sanctuary city', a term used by Donald Trump for cities which refuse to detain illegal immigrants for deportation.
Its Mayor Michael Hancock embraced the title earlier this month despite threats from the president to cut federal funding to cities and states that don't comply with his plans for immigration and deportation.
Read more here.