During day four of the hearing, evidence was given by Det Con Robert Barr, who was involved in cell site analysis as part of the investigation into the bombing.

BBC: Omagh bomb scene

In addition to Walker, five witnesses testified Thursday morning, including officials with cell phone companies and a computer forensic specialist for the Ohio Bureau of Investigation who testified about her analysis of the contents of 17 cell phones examined by police.

CNN: STORY HIGHLIGHTS

After gathering enough evidence to get a court order to investigate Kruse Wellwood, 16, and Cameron Moffat, 17, police bugged their homes, monitored their cell phones, and performed forensic analysis of their computers and phones for a history of their Internet activity and online and text conversations.

FORBES: Solving A Teen Murder By Following A Trail of Digital Evidence

The prosecution must also supply the defense a chain of custody, a list of tests performance and any reports generated when prosecutors sent Martin's cell phone to California to get help unlocking it for analysis.

NPR: Fla. Judge: No Trial Delay In Trayvon Martin Case

The defense is disputing the agent's analysis, saying the cellphone calls can be initially routed through cell towers blocks or even miles away.

WSJ: Cannibal-Plot Trial of Cop Tests 'Fantasy Defense'