Homicide detectives arrested the boy at his home. The boy, whose name was not released, was charged as a juvenile.
Maryland's assisted-suicide law, which took effect Oct. 1, was aimed at physician-assisted suicides. Under the law, anyone who provides the physical means another person uses to end his or her life faces a maximum of a year in prison and a $10,000 fine.
Kristen Riggin, a spokeswoman for the state's attorney's office, said the boy provided the .38-caliber handgun that Jennifer Garvey, 15, used to kill herself on Oct. 18 in a culvert in Crofton. The gun had been stolen from the boy's stepfather, Riggin said.
The couple left a note to their family and friends, in Jennifer's handwriting, that read in part: ``You've kept us apart and hurt us with your insensitivity. Now we can be together.''
Jennifer, who was being treated for depression, went through with the pact as the boy watched, prosecutors said. But the boy ran to a nearby friend's home.