(CNN) -- The Chicago police union again is calling for a federal investigation into State's Attorney Kim Foxx to determine the extent of her involvement with the Jussie Smollett case.
Kevin Graham, president of the Chicago Fraternal Order of Police, said the demand is based on news reports about text messages between Foxx and an attorney about, according to him, "diverting the case from Chicago police department to a federal investigation."
Foxx, the state's attorney for Cook County, recused herself from the Smollett investigation in mid-February.
Graham, who spoke to reporters after prosecutors announced they were dropping charges against Smollett, said he originally made the request to the US Department of Justice last week. He also has asked federal investigators to look into a letter sent to Smollett days before he alleged he was attacked on a Chicago street.
"We're doubling down on that. We want to make sure that the Justice Department takes a very hard look with that case and what went on today," he said.
Text messages obtained by CNN through an open records request show Smollett family friend Tina Tchen -- a former chief of staff for first lady Michelle Obama and a lawyer -- reached out to Foxx on February 1. Tchen wrote the family had "concerns about the investigation."
Foxx emailed Tchen saying in part, "Spoke to Superintendent Johnson. I convinced him to (r)each out to FBI to ask that they take over the investigation. He is reaching out now and will get back to me shortly."
Later another person, identified by Foxx's office as a family friend, asked the prosecutor whether they could talk on the phone. She says Tchen gave her Foxx's number.
Hours later, Foxx texts the unidentified family friend that she "spoke to the (police) superintendent earlier, he made the ask. Trying to figure out the logistics."
The person responds: "Omg this would be a huge victory."
The text message exchange went back and forth with Foxx and the family friend until Feb. 13 and these messages are why Foxx recused herself from the investigation, Cook County State Attorney's Office spokeswoman Tandra Simonton said earlier this month.
CNN reached out to Foxx on Tuesday but didn't get a response.
Efforts to get a comment from the Department of Justice on Tuesday night were also unsuccessful.