Referring to still and video pictures displayed on a large screen in a darkened courtroom, a Suffolk County crime lab supervisor Thursday led a jury in a Riverhead courtroom down a 370-foot trail of blood left by a dying Ecuadorean immigrant as he stumbled away after seven teenagers attacked him in Patchogue on Nov. 8, 2008.

Joselo Lucero - the brother of Marcelo Lucero, who was stabbed during the attack - watched intently as Donald Doller, a crime lab forensic scientist, answered a prosecutor's questions and described what was in the photos.

Doller was testifying in the hate-crime trial of Jeffrey Conroy, 19, of Medford, who was one of the teenagers in the gang. Conroy faces second-degree murder and first-degree manslaughter charges in the death of Lucero, 37. The case has attracted international attention.

Some of the pictures the jurors saw showed the hot-pink marking paint that Doller sprayed along the trail of blood after arriving at the crime scene.

"I marked the trail so that in photographs, the trail would be more visible," Doller said.