LATEST STORY: The third teen was taken into custody overnight Friday.

Two high school freshmen were arrested in connection with the killing of a man walking his dog last week in Philadelphia’s Overbrook section. A third teen, who police say actually pulled the trigger, is still on the loose.

Brandon Smith, 15, was arrested Thursday and charged in the murder of James Patrick Stuhlman, who plead for his life before he was gunned down while walking his dog along the 6400 block of Woodcrest Avenue last Thursday night, police said.

The teen who's under arrest, however, was not the shooter, said Philadelphia Homicide Captain James Clark.

A second 15-year-old, Tyfine Hamilton, fired the shot that resulted in the death of the 51-year-old husband and father, said Clark. He's still at large and considered armed and dangerous, police said.

"Get with your parent and turn yourself in before we come and get you," warned Clark during a news conference Thursday afternoon. "We know where you are."

Both teens were known to officers from previous crimes. A third teen, a 14-year-old, was charged with robbery, but was only a witness to the murder, police said.

Earlier Thursday, officials announced a $20,000 reward for information leading to the arrest of the killer.

Police say that the teens were playing basketball when they decided to rob someone. Initially, they targeted a different man walking his dog until they saw Stuhlman who was older and whose dog looked "weak."

The teens approached the man and annouced a robbery. A slight struggle ensued and that's when the man was shot once in the chest, according to officials.

"At one point he did plead for his life," said Clark. "He said, 'please don't shoot me, please don't shoot me,' and they still shot him one time."

Stuhlman took his nightly walks with the family dog, often with his daughter, authorities said. Police found him unresponsive at the scene, the dog leash still in his hand, said Philadelphia Police Lt. John Walker.

"The dog was lying next to him -- appeared to be scared and in shock," Walker said. "In his other hand he had a flashlight."

"His daughter goes for a walk with him almost every night," added Clark. "For whatever reason, he said to her, 'it's a little late tonight I don't want you walking with me.' So in effect, he may have saved his daughter's life."

Medics rushed Stuhlman to Presbyterian Hospital, where he was pronounced dead.

Stuhlman owned Hilltop Distributors -- a Delaware County landscaping company -- with his brother Mike. He left behind his daughter, wife Theresa and six siblings. He was laid to rest Wednesday morning.

Overnight Wednesday, authorities questioned six people and also searched a home on the 6500 block of Girard Avenue where they confiscated several guns. They have yet to determine if one of those weapons was used in the crime.