CHICAGO (CBS) — Federal prosecutors have sought the stiffest sentence possible for a purported gang leader convicted of drug trafficking, arguing he was the triggerman in the murder of a Chicago cop and his female friend.

WBBM Newsradio’s Bernie Tafoya reports convicted drug dealer Jason “J-Rock” Austin was charged in 2008 with killing Officer Robert Soto, and his friend, Kathryn Romberg, as they sat in an SUV on the West Side.

But charges against him were dropped when witnesses against him changed their stories, and pointed the finger at someone else.

Now, federal prosecutors have said they’ll try to prove Austin was indeed the gunman, when he faces sentencing later this year. In a pre-sentencing filing, prosecutors said they’ll prove Austin made calls while in Cook County Jail to arrange for witnesses against him to be intimidated.

In one of the calls, Austin allegedly admitted he was at the scene of the double murder.

The federal government alleges Austin and gang underlings sold thousands of dollars of heroin a day, and are seeking to have him locked up for 40 years.