Crossing the border illegally in the searing summer heat is lethal — about 2,000 bodies have been found in Southern Arizona's desert since 2001.

Few carry identification, and the effects of the sun and animals leave many bodies unrecognizable.

Figuring out how they died is the easy part — in most cases their internal temperatures rose so high they became delirious, fell unconcious and died. But determining who they were is a difficult, often gruesome task, that has transformed the Pima County Medical Examiner's Office.

There are so many bodies that taxpayers are paying for more staff and an extra storage cooler.

Summer, when the dead arrive daily, pushes the forensic scientists to their limits as they try to solve each mystery, and find answers for families desperate for word of their missing loved ones.

The special section that ran as a print exclusive Sunday is now available to online readers.

Nearly 1,700 bodies, each one a mystery

Nearly 1,700 bodies, each one a mystery

Photo gallery: A decade of death

Arizona's international border
Illegal immigrant deaths, by Border Patrol sector

Star border and immigration reporter Brady McCombs previews the series

Interview excerpts with Dr. Bruce Anderson, forensic anthropologist with the Pima County Medical Examiner's Office
Interview excerpts with Robin Reineke, a University of Arizona anthropology graduate student who has worked at the Pima County Medical Examiner's Office for four years

Search a database of individuals who have died attempting to cross the U.S.-Mexico border

July proved deadly month for migrants (Aug. 3, 2010)
Patrol's 'Mr. 911' juggles phones, emotions to save border crossers (Aug. 23, 2009)
Death count rises with border restrictions (May 17, 2009)
'Deadliest migrant trail in U.S.' is right on Tucson's doorstep (Dec. 9, 2007)
Death in the desert: Jesús' long journey home (Sept. 30, 2007)
July is deadliest month for illegal-entrant women (Aug. 3, 2007)
Efforts to cut summer deaths along border aren't working (June 24, 2007)