It was during the peak of the homebound commute, witnesses said, that they saw a dangerous "cat-and-mouse game" in which two motorists were jockeying for positions on a quarter-mile stretch of highway where two lanes become one.

When it was over, an 18-year-old college-bound Chester County girl was dead, her family and friends were devastated, and a nationwide manhunt had begun for the driver of a faded red pickup who shot and killed Bianca Roberson in what police said was a road rage murder.

"This homicide was completely senseless," said West Goshen Police Chief Joseph Gleason. "A beautiful young lady of 18 years of age, in the prime of her life, getting ready to go off to college. And for reasons that are incomprehensible to me, the family is now planning her funeral instead of a going-away party for college."

More than 20 investigators were sorting through hundreds of leads by email and phone from across the country, collecting video clips, and canvassing the streets for clues to what happened on the Route 100 bypass at about 5:30 p.m. Wednesday. Police Capt. Gregory Stone called the incident a "heartless" act unlike any he'd witnessed in his 32-year career.

Tips flowed in steadily after Chester County District Attorney Thomas P. Hogan announced Thursday night that Roberson's killing had become a murder investigation, Stone said.

"It's going to take a tip from a concerned citizen, a neighbor of the individual, a coworker of the individual, who finally puts two and two together, with a description of the vehicle, and the description of the gentleman, and knowing that this person has a firearm," he said. "We're also hoping this gentleman turns himself in to us or comes forward with his attorney."

Police released a composite sketch of the suspect late Friday, assembled with the help of a motorist whose vehicle was for a time adjacent to the pickup truck, Gleason said.

Witnesses described the shooter as a white man of medium build with blond or light brown hair, in his mid-20s to early 30s. The pickup appeared to have tinted back windows, said Michael Noone, the first assistant district attorney.

Roberson was driving south on Route 100 near where it approaches Route 202, Hogan said. Police found her in her green Chevrolet Malibu after it crashed off the road.

Police have retrieved and reviewed video footage from PennDot cameras just moments before the shooting, Noone said. Still images can be viewed on the Crime Stoppers webpage.

Rodney Roberson, the victim’s father, said Friday that his daughter had been at Exton shopping for school supplies and groceries with her mother and grandmother. She left the mall to drop off some things at home before heading out to meet friends, he said. Her grandmother took the same route home from the mall a little while later and passed the crash scene — and the commotion of police and fire trucks — not knowing that it involved Bianca.

"We are trying to come to grips with this," Roberson said, "because she wasn't the type of person you'd go up to and shoot."

At the Robersons' brick townhouse in West Chester, a flower delivery was dropped off and several of the girl's friends pulled up to visit. Diana Williamson, 18, of Brookhaven, and Sydney Miller, 19, of Media, said that the victim's coworkers at White Horse Village retirement community in Newtown Square were stunned by the tragedy.

Bianca Roberson "was super-lovable," Williamson said. "I don't think she hated anyone."

Miller said Roberson was ridiculous in the best way and "just the funniest person."

She was full of energy, the girls recalled, and the type of person who would answer a 2 a.m. call or text from a friend in need. When friends had relationship problems, Roberson was always the first to defend them and remind them of the treatment they deserved, Williamson said, starting to cry as she spoke.

Another friend from work, Jordan Yates, 22, of Media, described Roberson as a hard worker and said they'd become friends, attending concerts and watching scary movies together when they weren't running food to the chafing dishes for the elderly residents at the White Horse Village buffet table.

"If I got kicked out of my house and I had nowhere else to stay, she would stay in the car with me," Yates said. "If I didn't have a T-shirt to wear or my T-shirt was ripped, she would get her shirt off her back. I don't know anybody else like her."

At Bayard Rustin High School, from which the victim had just graduated, assistant principal Joe DiAntonio remembered Roberson on Friday as a caring and enthusiastic student and a friend to many. Roberson grew considerably during her four years at Rustin, getting involved in the black student union and winning the Knights of Character award for citizenship, he said.

And she was ecstatic to begin classes at Jacksonville University in the fall.

"She was so ready to take that next step," DiAntonio said. "I can't put into words the loss of a young person with so many things in front of them."

The high school offered counseling to students Friday, and several students and three staff members had taken advantage of it, said Leigh Ann Ranieri, director of pupil services.  She said the school would continue to offer services next week.

Roberson's family members, meanwhile, appealed for anyone with information about the driver in the red pickup truck to go to the police.

Authorities on Friday announced a $5,000 Crimestoppers reward and urged anyone with information to contact police at 610-696-7400 or detectives@westgoshen.org.

"This is going to come down, ladies and gentlemen, to assistance by the public," Gleason said. "The family deserves this. Society in general deserves this."