Murtha said in an interview last week that the seriousness of the charges weigh against the transfer request, "so the other factors have to be very compelling."

Much will depend on the recommendation of the Maryland Department of Juvenile Services, which has conducted several interviews with Morgan Arnold. An agency spokesman said those recommendations are not made public.

It is common practice for defense lawyers to request transfer on behalf of juveniles charged as adults, but it is difficult to say how often they are successful. No statewide statistics have been compiled, said Jason R. Tashea, juvenile justice policy director for Advocates for Children & Youth.

The organization did a study limited to Baltimore, focusing on juveniles charged as adults from 2009 through 2011. During those three years, 907 juveniles were charged as adults and 255, or 28 percent, were granted transfer to juvenile court.

James Johnston, who heads the juvenile unit of the Baltimore City office of the public defender, said his office has stepped up efforts on behalf of juveniles eligible for transfer. In 2013, he said, 80 percent of its transfer requests were approved.

In his experience, said Baltimore County State's Attorney Scott D. Shellenberger, juvenile defendants charged as adults in extremely violent crimes usually do not have their cases transferred to juvenile court. The law now names 33 crimes — most of them violent — that are automatically handled in adult court.

Shellenberger represented Maryland prosecutors last year before the task force that is considering the juvenile court's role and making recommendations to lawmakers. He argued in favor of retaining the current system.

"These aren't children," Shellenberger said in an interview. "These are criminal defendants who in many cases have committed a very violent and heinous act."

Shellenberger declined to comment on Arnold's case, but he mentioned her in his PowerPoint presentation before the task force. He added her photograph to a gallery of notoriously violent cases involving juvenile defendants. He also included Nicholas W. Browning, who was sentenced at age 16 to four life terms for killing his parents and two brothers at his home in Cockeysville in 2008.

Browning was denied a transfer request, as were most of the 14 teenagers that Shellenberger mentioned in his presentation, including three youths who violently assaulted staff members after they were committed to detention centers run by the Department of Juvenile Services.

Shellenberger argues two main points: The juvenile system is not equipped to hold violent defendants before trial, and the juvenile system can hold youths only until they turn 21, which in many instances is not sufficient punishment.

"Do you want Nick [Browning] released after just six years in a juvenile detention facility?" he asked in his presentation.

Advocates for juveniles say the practice of charging youngsters as adults stems from a crackdown on violent crime that emerged in the late 1980s and 1990s — and it has failed. They point to national studies which show that young people who are sent to adult prisons become more dangerous than those who were committed to juvenile services.

Johnston, the public defender in Baltimore City, said the current system "runs counter to both common sense and what scientists know about adolescent brain development. ... The fact is, children are different."

He points to three Supreme Court decisions since 2005 that recognize the evidence for this distinction, including cases in 2010 and 2012 that limited the use of mandatory life sentences for juveniles.

In the 2010 case, Justice Anthony M. Kennedy wrote that the failings of an adult and a juvenile should not be equated, "for a greater possibility exists that a minor's character deficiencies will be reformed."

Cindi Arnold agrees.

"What kind of world do we want to create," she asked, "where we put children in prison and don't see them as humans with potential?"