The twin blasts that marred the Boston Marathon on Monday, killing three and injuring 175 bystanders, also left behind gruesome clues in the form of shrapnel embedded in victims.
As Boston trauma surgeons treated wounds, they were not only caregivers but evidence collectors, reportedly removing BB pellets, ball bearings and nails from victims in the operating room. The removed shrapnel could provide key clues in the ongoing investigation into the bombing.
At Massachusetts General Hospital, which treated 31 patients , Dr. George Velmahos, division chief of Trauma, Emergency Surgery and Surgical Critical Care, said some victims had multiple wounds caused by "nails or sharp objects."
"Many victims had 10, 20, 30 of them in their body or more," said Velmahos. "[We're] working very closely with investigators and we have handed over whatever evidence we can find."
Surgeons treating patients with traumatic blast injuries have to walk a fine line by only removing shrapnel that is safe to remove, even if it is needed evidence in a criminal case.
Oscar Guillamondegui, trauma medical director at Vanderbilt University (who did not treat any victims of the Boston bombing), says medical staff does not usually remove shrapnel unless it is easily accessible or an immediate danger to the patient's health.
"It's a tough balance, in the world of [trauma surgery,]" said Guillamondegui. "The last thing we want to do is go digging into someone."
By unnecessarily removing shrapnel or foreign material embedded deep in the tissue, Guillamondegui says there can be a risk of nerve and muscle damage to the patient.
However, if it is safe to remove, the piece of shrapnel or a ballistic fragment is generally sent to the hospital's pathology department, which tags the evidence and sends it to the appropriate law enforcement office if necessary.
In rare cases, Guillamondegui says shrapnel can be removed at a later date if law enforcement officials need it as evidence or if it is causing a patient continued pain, providing it becomes more accessible.
Although the FBI will not comment on evidence collection, Dr. Lawrence Kobilinsky, chair of the department of sciences and a forensic scientist at John Jay College, in New York City, says investigators can potentially use metal fragments taken from victims to piece together the bomb in order to find the perpetrator.
"You want to reconstruct the bomb. You want to know how many nails or ball bearings were in the bomb," said Koblinsky. "They don't disappear; whatever you put in [a bomb] has to come out."
Koblinsky says metallurgists can look at the characteristics of the metal in the bomb and in the nails, ball bearings and BB pellets in order to find their manufacturer.
"If you can narrow down, you can individualize, you have a better opportunity to figure out who manufactured it [and] who bought it," said Kobilinsky. "All these little leads are going to add up to a big lead."