Arrest made in shocking killing of New Orleans 1-year-old Londyn Samuels

Londyn Samuels, 1, was struck by a bullet fired into her 18-year-old nanny's back Friday in New Orleans. Courtesy Keion Reed

A 24-year-old man was arrested Wednesday and booked on suspicion of first-degree murder in the shooting death of 1-year-old Londyn Samuels, whose killing stunned the city and the nation last week, police said.

Keelen Armstrong, 24, was arrested in Londyn's killing after he was pulled over for speeding and found to have outstanding warrants, Superintendent Ronal Serpas said at a news conference at police headquarters. He said a second suspect was being sought.

Serpas said nothing about a possible motive, and he wouldn't say how police connected Armstrong to the killing.

Serpas also announced a major development in a second shocking homicide, saying authorities had identified a "person of interest" in the death of 11-year-old Arabian Gayles, who was shot along with her cousin and an unidentified man Monday morning.

Mayor Mitch Landrieu declared "enough is enough" after Londyn, who was just learning to walk, was struck by a bullet fired into her 18-year-old nanny's back as she carried the toddler home from the park Friday.

Two shots were fired, one of which ripped through the nanny's torso and hit Londyn in the chest. In addition to the murder count, Armstrong was also held on suspicion of attempted first-degree murder.

Keelen Armstrong was arrested Wednesday on suspicion of murder and attempted murder in the shooting death of Londyn Samuels, 1, and the wounding of her 18-year-old nanny. New Orleans Police Department

The nanny, who was expected to survive, called the child's father in anguish.

"She said, 'Kee, we got shot — me and Londyn,'" Londyn's father, Keion Reed, 20, told NBC News this week.

Police said two men were seen running from the scene. They said that there was no gunfight and that the two victims weren't caught in any crossfire.

In a statement, police said Armstrong was pulled over for speeding on Interstate 10 Wednesday morning. He was taken into custody for driving with a suspended license and on an outstanding warrant from nearby Gretna. The nature of the charge in Gretna wasn't disclosed.

While Armstrong was in custody, officers determined that he was also a suspect in the shootings Friday. 

"This is an example that there is no such thing as a routine traffic stop," Serpas said Wednesday night.

Angela Robertson, a family friend and spokeswoman, told NBC News on Wednesday night that "we are not sure of the motive or who this person is," but she said, "It is a relief for us to know that the monster is locked up."

In the second case, police were seeking Keith Ward, 33, as a person of interest in the death on Labor Day of Arabian and the shootings of her cousin Paulreiona Cary, also 11, and a 38-year-old man whose identity still hasn't been released.

Serpas stressed that Ward was being sought because he might know something about the shootings — not because he was necessarily a suspect.

Arabian was remembered at a vigil Tuesday night near her New Orleans home.

Four young children were in the home where Arabian was, chillingly, holding a 1-year-old in her arms when gunman opened fire outside. Police have said multiple gunmen got off more than a dozen rounds but haven't said anything about a motive in that case.

Derek Moffett, Arabian's uncle, said he ran to the young girl when the bullets started flying, but he was too late.

"When I woke up, I heard them screaming," he told NBC station WDSU of New Orleans. "I jumped out of my sleep. I ran over, I grabbed her, touched her. She wasn't breathing."

NBC News' Tracy Connor and Matthew DeLuca contributed to this report.