Federal investigators trying to piece together the twisted trail that led accused Charleston church gunman Dylann Roof to kill nine worshippers last week reportedly served subpoenas on phone and Internet providers Tuesday. 

With the surfacing of a "manifesto" believed to have been written by Roof and posted on a website registered to him, authorities believe digital communications could help them learn about possible influences and provide a clearer timeline of events that led to the shooting, ABC News reported. In addition to posting pictures of himself at several Confederate landmarks and waving the Confederate flag, Roof appears to have been obsessed with high-profile, racially charged cases that made national news in recent years, including the Florida case in which unarmed teen Trayvon Martin was shot dead by George Zimmerman.

"It was obvious that Zimmerman was in the right, Roof wrote. "But more importantly this prompted me to type in the words "black on White crime" into Google, and I have never been the same since that day."

Roof was charged with nine murder counts after the shooting at the storied Emanuel African Methodist Episcopal Church in Charleston. He was captured over 200 miles away in North Carolina and has been held at the Al Cannon Detention Center in Charleston. In addition to the potential death penalty charges in South Carolina, the Department of Justice has opened up a hate crimes investigation of Roof, and his Internet communications, if authenticated, could be evidence his act was motivated by racial animus. 

The high school dropout had a history of drug use and appeared to be directionless in life and may have been self-radicalized. In the manifesto, he uses the "n-word" repeatedly to describe African-Americans and criticizes white for moving to the suburbs "because they are too weak, scared, and brainwashed to fight."

A friend of Roof's told the The New York Times that Roof was fixated on the Trayvon Martin case and that the reference to it almost confirms that Roof penned the manifesto.

Beside the manifesto, a woman who spoke to a witness told NBC that the gunman at the church, who attended the meeting for an hour, asked to sit next to the pastor and said, "I have to do it. You rape our women and you're taking over our country. And you have to go."

The pictures of Roof posing with the Confederate Flag prompted calls in South Carolina for the removal of the flag from statehouse grounds.

"The time has come," Gov. Nikki Haley said. "That flag, while an integral part of the past, does not represent the future of our great state."

The Republican governor said taking the flag down would unite the state.

"We are not going to allow this symbol to divide us any longer," she said. "The fact that people are choosing to use it a sign of hate is something that we cannot stand. The fact that it causes pain to so many is enough to move it from the capital grounds. It is after all a capitol that belongs to all of us."

The Sons of Confederate Veterans said it plans to vigorously fight any effort to remove the Confederate flag from the grounds.