On December 16, 2006 a four month old boy was killed and his mother was seriously injured after a tractor trailer rammed into their vehicle. It happened over a month ago but police are still conducting their investigation, trying to figure out just how fast the 18-wheeler was going. Saturday morning Shreveport Police Department`s Crash Investigation Unit blocked off Interstate 20 near the Hearne Avenue exit. For nearly three hours, investigators worked to reconstruct the scene of the fatal accident. Officers marked off roadways and used a laser to help create a scale diagram of the crash scene. "We have a person out there with a prism on a pole. Gives us elevation.. Gives us the distance from the point where I am to where he is. That puts it into a program where he can draw a scale diagram," said Corporal Bill Vincent. Once the scale model is complete, the findings will be presented to the District Attorney`s office. "It`s a fatality. Charges may be brought up, depending on what I find out when I do my calculations," said Corporal Bill Vincent.