A mangled double baby stroller, pairs of impossibly tiny, colorful children's sneakers, flip-flops, women's shoes, and a handbag.

The remnants of the horrific final seconds of Samara Banks and three of her children sat in a corner of the Philadelphia courtroom Tuesday as the nonjury trial continued of the alleged drag racer who killed them.

The personal effects were a sobering counter to a day of technical testimony by Officer William Lackman, a police accident-reconstruction expert.

Lackman spoke of skid marks, debris fields, and "body throw weight" - the speed Khusen Akhmedov's silver 2012 Audi S4 had to be traveling to propel the body of the 27-year-old Banks 210 feet south from impact on the southbound Roosevelt Boulevard at Second Street.

Police said Akhmedov, 24, was drag racing with Ahmen Holloman, 32, who was driving a souped-up white 1994 Honda Civic, when Akhmedov lost control and plowed into Banks and her four children at 79 m.p.h. as they struggled to cross the 12-lane highway.

Banks and three of her sons - Saa'mir Williams, 7 months; Saa'sean Williams, 23 months; and Saa'deem Griffin, 4 - were killed. Banks' oldest son, 5-year-old Saa'yon Griffin, survived.

On Monday, Holloman pleaded guilty to four counts of vehicular homicide and was sentenced to five to 10 years in prison.

Akhmedov elected a nonjury trial before Common Pleas Court Judge Steven R. Geroff after Assistant District Attorney Thomas Lipscomb agreed not to seek a mandatory life term if Akhmedov is found guilty of more than one count of third-degree murder.

Defense attorney Michael Diamondstein has conceded that his client was driving too fast and that his car struck and killed Banks and the children.

Diamondstein, however, insists that Akhmedov did not have the malice - legally, a "hardness of heart" or "sustained recklessness" - to support a third-degree murder verdict. Diamondstein argues that Akhmedov should only be found guilty of the lesser crimes of involuntary manslaughter or vehicular homicide.

Questioning Lackman, the defense lawyer elicited the fact that Akhmedov legally owned the Audi, had a license, was insured, and did not leave the scene.

Mostly, Diamondstein focused on the design of the Boulevard and its reputation as one of the region's deadliest highways.

Using photos and maps, Diamondstein pointed out that Banks and her children crossed in an area not designated for pedestrian crossings. Still, he noted, a concrete path led from the sidewalk across the two median strips and all 12 lanes of traffic.

Lackman said that path has since been replaced with grass.

Diamondstein also presented his own blown-up version of a surveillance video of the accident from a camera at an auto lot.

Lackman testified that the video did not show the impact, just Akhmedov's Audi careening across several southbound lanes and the grass strip adjacent to the sidewalk before taking out a street sign and stopping in a southbound lane.

But in the version Diamondstein showed in court, several shadowy figures are seen crossing the outer southbound lanes until they are lost in the glare of the Audi's headlights. There is a flash of light and sparks, and the Audi continues on its way.

"I never saw [the figures] before," said Lackman, who said he had viewed the video six times.

Lipscomb, the prosecutor, objected to the defense video's relevance to Akhmedov's culpability in the four deaths.

Diamondstein argued that his client's speed was just one factor in the fatal accident.