Winfree conceded that it currently takes between 11 and 17 days to analyze DNA, but the information could still be used to modify bail decisions. She added that the FBI estimates that within two years it will be possible for police to analyze DNA profiles within 90 minutes.

"This is not science fiction," she said. "This is the finger printing of the 21st century, but it is better."

Kannon K. Shanmugam, a lawyer for King, who was convicted of a 2003 rape after his DNA was taken a 2009 assault arrest, suggested that the government is really more interested in solving old cases.

He said there have been no instances of bail or other pretrial decisions' being altered since Maryland adopted its new system.

It's also not clear whether under current Maryland law the DNA could be used in that way. The statute says the profile cannot be compared with others in the database until a suspect has been arraigned, which typically happens after an initial bail decision is made.

"If the government were to come back in five years' time with a DNA testing program the primary purpose of which was pretrial supervision or identification … then sure, the analysis would be different," Shanmugam added.

Roberts suggested, though, that it might not be proper for the court to decide based on some future technological standard.

"How can I base a decision today on what you tell me is going to happen in two years?" he asked Winfree. "You say, in two years we will have this rapid DNA available, but we don't now."