The toddler and her little brother had been home with their mom when the attacker struck.

The young mother was stabbed repeatedly late Sunday by an ex-boyfriend in her Lansing apartment before she managed to get away -- and call law enforcement, the Michigan city's police chief and the FBI said.

Little Wynter Cole-Smith's 1-year-old sibling soon was found unharmed in the apartment, the bureau said.

But his 2-year-old big sister -- in a white T-shirt with rainbows, her hair in braids to her shoulders -- was gone.

Lansing Police early Monday issued an AMBER Alert, blitzing cell phones, radios, TVs and road signs to aid their search for Wynter and suspect Rashad Maleek Trice, possibly in a white 2013 Chevy Impala.

Alerts like these, the National Center for Missing & Exploited Children says, "are usually resolved within hours."

And indeed just before dawn Monday, Trice crashed a stolen Impala some 90 miles from Lansing in St. Clair Shores, Michigan, and was taken into custody, the FBI said.

But Wynter wasn't with him.

Lansing police, with the FBI and others, knocked on doors and deployed search dogs. They asked strangers for doorbell surveillance videos, launched helicopters with heat-signature technology and drones, even called in a dive team, Chief Ellery Sosebee said Tuesday at news conference.

But no little girl.

"Wynter is one of our kids," the chief said as families across America gathered to celebrate the Fourth of July. "And we won't rest until we find her."

The FBI announced a $25,000 reward for information to locate Wynter.

The hours dragged on.

"We just want to find her," Wynter's dad told the Detroit Free Press on Wednesday. Her 22-year-old mom, whom authorities have not named, was nearby as volunteers swept a suburb north of the city hoping to find their daughter, the newspaper reported.

Still, not a trace.

Then that evening, FBI agents made a discovery.

Offering scant details, FBI Acting Special Agent Devin Kowalski told reporters: "This is not the outcome we were hoping for."

"We are devastated by the tragic news that Wynter Cole Smith was found deceased today," Ingham County Prosecutor John Dewane said in a statement. "Our hearts are with Wynter's family as they begin to process and grieve the unnecessary loss of a beautiful two-year old child."

The investigation, he said, had transitioned from a missing person case to a homicide inquiry.

Trice, 26, has been charged with felony assault with intent to murder, first-degree criminal sexual assault, first-degree home invasion and other crimes, state court records show.

Trice, through his attorney, declined to comment. He is being held without bond, with a probable cause hearing set for July 13.

Now, Wynter's relatives are planning a Friday evening vigil.

"We are heartbroken over the loss of our beautiful daughter, granddaughter, cousins, niece and big sister," her family said Thursday in a statement.

"Wynter's brief but bright life was taken from her unnecessarily; and we will grieve her death forever."