The U.S. Department of Justice and FBI have begun an investigation into the case of Trayvon Martin, the 17-year-old unarmed black boy who was shot and killed by a neighborhood watch captain in an Orlando suburb.

The department will conduct a thorough and independent review of all evidence and take appropriate action at the conclusion of the investigation, the department said in a statement late Monday.

The department also is providing assistance to and cooperating with the state officials in their investigation into the incident. With all federal civil rights crimes, the government must prove beyond a reasonable doubt that a person acted intentionally and with the specific intent to do something which the law forbids - the highest level of intent in criminal law, department said.

Negligence, recklessness, mistakes and accidents are not prosecutable under the federal criminal civil rights laws.

The investigation announcement came following a day of protest and rally demanding the arrest of watch captain George Zimmerman.

On Feb. 26, Zimmerman gunned down Martin as he was walking through a gated community to buy candy and iced tea at for his brother. Zimmerman later told police that he had fired in self-defense. Martin, who lived in Miami with his brother, died from a gunshot wound to the chest.

However, Zimmerman was questioned by police and was released without any charges. According to police, the 28-year-old had license to carry a gun and no evidence was found against Zimmerman self-evidence claim.

Martin killing case has attracted national attention and has also raised concerns among civil rights leaders.

On Monday collage students organized rallies in front of a criminal court building in Sanford and also on the campus  of Florida A&M University in Tallahassee calling for the arrest of Zimmerman.

Civil rights leader Al Sharpton is also expected to plan a rally at a Sanford church on Thursday.

Martin's parents, Tracy Martin and Sybrina Fulton, in a press conference  Friday said that they no longer trusted the Florida police and want the FBI to handle the case now.

I feel betrayed by the Sanford Police Department and there's no way that I can still trust them in investigating this crime, Tracy Martin said.

Martin's parents and other advocates have said the shooter would have been arrested had he been black.

The department of justice opened the investigation in response to an international petition, celebrity tweets and spreading public outrage.   

Tweets from movie director Spike Lee and musician Wyclef Jean and other celebrities over the weekend made #Trayvon a trending topic on Twitter.

According to Miami Herald, Martin's parents blamed Sanford police of molding the investigation. Several witnesses said that they heard screams cries and shots of gunfire.   

However, Robert Zimmerman, father of Zimmerman, wrote a letter to the Orlando Sentinel denying his son had followed or confronted Martin.

He said his son was a Spanish-speaking minority with many black family members and friends.

He also said that the portrayal of Zimmerman is false and extremely misleading.