BALTIMORE >> Investigators are focusing on speed as they delve into the collision between a school bus and a commuter bus that killed both drivers and four mass-transit riders in southwest Baltimore.

Baltimore Police Department spokesman T.J. Smith said Wednesday investigators haven’t yet determined how fast the vehicles were going when the school bus crossed the center line and smashed into the Maryland Transit Administration bus early Tuesday morning after hitting a car and a roadside pillar.

“If you saw that destruction, it certainly wasn’t caused by a slow-moving vehicle,” he said.

In a recorded 911 call, a man who gave his name as Cameron said, “The school bus was going 90. The school bus tore off the street and kept on moving.”

The National Transportation Safety Board tweeted a photo of its investigators doing a three-dimensional scan of the mangled school bus, which wasn’t carrying any children.

Smith said police plan to interview the only passenger on the school bus, an aide who had minor injuries.

He said it could be weeks before investigators get an autopsy report that could reveal whether school bus driver Glenn R. Chappell, 67, of Baltimore, suffered a medical emergency.

Investigators have recovered recording equipment from the MTA bus but don’t know if it’s in usable condition.

Chappell was found at fault in three traffic-related cases in the last eight years, according to court records and an attorney interviewed by The Associated Press.

He lost a civil case over hitting a parked car in Baltimore in 2008. Nationwide Insurance said in its complaint that Chappell was distracted and speeding when his vehicle “veered from the roadway” and struck the car. The court ordered Chappell to pay about $2,400, which he did, according to Nationwide’s lawyer, Michael David Johnson.

Chappell was convicted in 2014 of failing to show a registration card during a traffic stop, and convicted again last November of driving a vehicle with suspended registration. Neither offense involved a school bus.

The records also show that Chappell was convicted of violating three protective orders issued in 2012. He spent much of the fall of 2012 in jail, awaiting judgment in those cases. In December 2012, he was sentenced to seven days for second-degree assault.

Chappell’s employer, bus contractor AA Affordable Transportation, didn’t respond Wednesday to calls and emails about Chappell’s legal problems.

Baltimore City Public Schools spokeswoman Edie House declined to comment.

Police released the names of five of the deceased, including Chappell and MTA bus driver Ebonee Baker, 33, of Rosedale. Smith said three of the 10 people injured remained hospitalized, in fair, serious and critical condition.

Baker’s mother, Helen Morgan, said her daughter was an outgoing, married mother of four who was living her dream: A family, a house with a pool and job driving a bus.

“I’m lost,” Morgan said. “This is unreal. This is my baby. I can’t believe this.”

She said Baker also was a Baltimore Ravens fan, an Overlea High School track coach and a skier.

“She helped so many kids because she was the coach of the track team that God needed someone in heaven to do better, so he took Ebonee so she could do better up there,” Morgan said.

Police identified three of the four deceased MTA bus passengers as Cherry Denise Yarborough, 51; Terance Lee Casey, 52; and Gerald Holloway, 51, all of Baltimore.