ANNAPOLIS, Md. -- Maryland prosecutors have asked a detention centre for copies of all mail to and from the man charged in the shootings of five Capital Gazette employees.

Prosecutors formally requested "certified copies of all incoming and outgoing mail" from Jarrod Ramos, who is charged with first-degree murder.

Public defender William Davis responded with a letter filed in court Thursday that he planned to "move to quash" the subpoena. Davis says it's "unlawful in its scope and constitutes a violation of the Defendant's constitutional rights."

Police say Ramos mailed threatening letters the day of the June 28 shooting. In one, he wrote that he was on his way to the newsroom with the aim "of killing every person present."