Solving a cold case murder investigation can be compared to working a puzzle. A multitude of pieces must come together to form one big picture.

Knocking on doors, re-interviewing witnesses and taking a second look at evidence are just a few of the ways that detectives can help find those missing pieces.

In "Cold Case Files" we have an exclusive first look at a clue in a North Central Florida murder investigation. This is the first time anyone outside the Alachua County Sheriff's Office has seen this important piece of evidence. There is no reminder along this rural Alachua County road that a murder mystery began here.

The victim was a young mom. On March 17, 2005, firefighters pulled the body of 34 year old Wende Ellinger from from her Kanapaha Highlands mobile home. That Thursday night, a neighbor had started to enter her burning trailer but says he stopped when he was told by another neighbor Wende wasn't home. It was a decision he would regret.

Wende was at home. She was dead. Investigators say the fire was started to cover up the crime.

Lt. Jack Jacobs of the cold case unit says Wende had been at the Gainesville Ale House just hours before her death. He believes Wende knew her killer saying, "It doesn't appear there is any sign of forced entry so we do believe she probably knew the person or expected the person that came to the trailer that night. There did appear there could be some sign of a struggle inside the residence."

Weeks later, a sign of a different type arrived at the Alachua County Sheriffs Office. And for the first time, we are able to show it to you. A one page handwritten letter on notebook paper mailed through a Gainesville post office. The letter was addressed to a detective at A.C.S.O.

It was postmarked April 30, 2005, and was signed, "Archer boy." In the letter there were certain details described that lead police to believe that person had information that would be relevant to the crime. Authorities say they're not sure of the identity of the person, but would be interested in speaking to that person. Authorities say they can remain anonymous.

The return address on the letter reads: "Archer Boy, 302 Magnolia Street, Archer FL." While the street is real, investigators could find no link to the case. In a deck that has been stacked against them, Lt. Jacobs hopes the "Archer Boy" letter will prove to be the trump card that solves this cold case.

If you know anything about the letter or this case, you are asked to call Lt. Jack Jacobs at Alachua County Sheriffs Office or call: 352.367.4000

There is a reward being offered.