A man and his cousin have been arrested on charges of conspiring to kill the man's 18-year-old girlfriend, who was fatally shot in front of the couple's year-old son during a staged mugging, authorities said.

Carlos Cruz, who was shot in the leg, and Devon Miller, 25, of the Bronx, were arraigned Tuesday night on first- and second-degree murder charges and pleaded not guilty.

"Obviously it's a troubling case for everybody involved, but my clients deny these allegations, and the truth will come out at trial," said defense attorney John Sandlaietner.

The alleged murder-for-hire plot unfolded Sunday afternoon when a man armed with a handgun approached Cruz's car in a secluded area in the Bronx and shot Chelsea Frazier twice in the torso. Witnesses said they saw Cruz chase the attacker, who turned and shot him in the leg.

Frazier was pronounced dead at the hospital. The couple's 1-year-old boy, Alijah, who was strapped into a carseat, was unharmed.

Police said Cruz, 36, of Southbridge, Mass., told them that Frazier got lost while she was driving and pulled over as the baby was fussing in the back seat. He said the shooting occurred after the gunman suddenly appeared and demanded his chain and money.

Investigators said they determined the mugger was Miller, and that he was paid $1,000 to kill Frazier and wound Cruz. Police said the killing was motivated by the couple's troubled relationship.