A 22-year-old Cheyenne man charged in the November 2017 shooting death of a 19-year-old has accepted a plea agreement from the U.S. Attorney's Office.

Armando Ramirez-Serna pleaded guilty Tuesday in U.S. District Court to interference with commerce by robbery and use and discharge of a firearm during and in relation to a crime of violence causing death, admitting that he shot and killed Justin Robinson and took marijuana and cash out of his SUV.

Robinson's body was found in a reservoir on the Wyoming Hereford Ranch on Nov. 26, 2017. His burnt SUV was found nearby.

In exchange for his plea, the government agreed to dismiss counts III and IV -- use and discharge of a firearm during and in relation to a crime of violence and use of fire to commit misprision of a felony -- during sentencing.

"This was a heinous crime," said Assistant U.S. Attorney Stuart Healy III, adding that Ramirez-Serna robbed Robinson of less than four ounces of marijuana and just over $200 to make a delinquent child support payment.

Healy said the plea agreement, which calls for a recommended sentence of 40 years, was reached over four weeks of discussion.

"We take this type of crime very seriously," said U.S. Attorney Mark Klaassen. "Obviously when you have a murder involved that's a particularly terrible and heinous crime, and so when we evaluate a sentence we want to make sure that justice is done."

Judge Alan B. Johnson ordered a presentence report and scheduled Ramirez-Serna's sentencing for Dec. 18.

Ramirez-Serna can withdraw his guilty plea if the court decides not to accept the plea agreement.