(CBS News) - The investigation into the killing of Trayvon Martin is essentially starting from scratch, with the new special prosecutor and a team of investigators quietly re-interviewing witnesses and examining evidence related to the unarmed teen's shooting death.
The 17-year-old Martin has been dead for a month, and George Zimmerman, his admitted killer, remains free after telling authorities he was forced to shoot Martin in self-defense.
The Sanford Police Department's lead investigator initially pursued manslaughter charges against Zimmerman, but was told by the state attorney that there wasn't enough evidence.
Here's what CBS News has pieced together from sources connected to the investigation.
On February 26th, the night Martin was killed, police questioned Zimmerman for five hours at police headquarters. The police report noted Zimmerman was "bleeding from the nose and the back of the head."
Police did not administer a drug and alcohol test or an immediate background check on Zimmerman, although they did both on Martin.
The next day, detectives re-enacted the shooting with Zimmerman at the scene. They also discovered Zimmerman had two prior arrests: one for assaulting a cop, the other for domestic abuse.
For the next two weeks, lead investigator Chris Serino pursued a manslaughter charge against Zimmerman.
Police interviewed at least six witnesses. But none of them saw how the confrontation began or the shooting that ended it.
Public pressure grew. On March 12, police gave the case to State Attorney Norm Wolfinger. He told them they needed more evidence to arrest Zimmerman.
Trayvon Martin's frustrated parents took their plea for justice to Washington Tuesday.
At a congressional forum on neighborhood watch groups and racial profiling, they thanked Democratic lawmakers for their support.
"As I said before, and I'll say it again - Trayvon was our son, but Trayvon is your son," Sybrina Fulton, Trayvon's mother said.
Now, acting Sanford police chief Darren Scott is trying to calm a firestorm of criticism that race played a role. "I would like to answer questions here, but I will not comment at this time."
Tuesday, Scott said Angela Corey, the new special prosecutor won't let him talk publicly about the case. "It's not in the police department's hands right now, ok?" Scott said. "I can't pass judgment right now on anyone right now, so we're going to allow the outcome of this investigation.
But to Martin's angry parents and their lawyer, Ben Crump, this is double-standard justice. "It's bad when George Zimmerman makes a bad decision to do things with a racial implication," Crump said. "But it's a tragedy when an institution of law enforcement does it because that's all we have to believe in. If that fails us, what can his parents do? What can they do?"