At the helm of what became "a battering ram on wheels," a cement truck driver killed a school bus driver, crippled a bus monitor, and disfigured an autistic child as he drove while high on Valium and using his cellphone, a prosecutor alleged Monday.

But Raymond Ragen's lawyer told jurors his client wasn't drug-impaired, and said police didn't do enough to try to find an SUV whose close encounter with his client's truck played a role in what led to the deadly Locust Valley collision in July 2012.

Ragen, 45, of Mineola, could spend up to 25 years in prison if jurors convict him of aggravated vehicular homicide following yesterday's closing arguments. They'll start deliberations Wednesday.

Authorities allege Ragen drove into an Oyster Bay Road railroad bridge that GPS records showed he knew was too low for his vehicle, before crashing head-on into a bus bringing special-needs students home from summer camp. Prosecutors said the GPS data showed Ragen had reversed course from the bridge earlier in the day.

The crash killed bus driver Jorge Guevara, a 45-year-old father of four. Bus monitor Louis Kragouras, now 65, previously testified he needed a hip replacement and a steel rod in his knee after multiple bones fractures from the crash.

Authorities said one of the four autistic boys -- all between 6 and 9 years old -- on the bus suffered a broken jaw and a detached lip, while the others had mostly minor injuries.

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Defense attorney David Besso said Monday that a sport utility vehicle had sideswiped or cut off Ragen's truck, causing him to hit his head and lose consciousness, before the cement mixer hit the bridge.

"If he hadn't hit his head, if he wasn't dazed, he wouldn't have gone down that road," Besso said.

He told jurors there were "hundreds of reasonable doubts" in the case against Ragen, calling the crash a tragedy that didn't involve any crimes. He claimed police stopped looking for the SUV when they didn't find tire marks or gouges, and didn't use fliers to seek information or canvass nearby for witnesses.

But Assistant District Attorney Brendan Ahern said a police investigation found no forensic evidence that another driver cut off Ragen, saying testimony from a bicyclist who was riding in the area backed that up.

Ahern also said Ragen couldn't have made it to the bridge if he was unconscious because he wouldn't have been able to navigate a turn in the road.

The attorneys also squared off about whether Ragen was drug-impaired, with Besso saying police would have arrested Ragen right away, not six months later, if there was any doubt about his sobriety.

The defense lawyer said two police officers, one at the scene, and another at the hospital, didn't find Ragen to be impaired.

But Ahern said while the amount of Valium was low, tests showed the drug was in Ragen's blood.

"You know this in your gut -- that if you take drugs like Valium, that it has a physical effect and it has a mental effect," he told jurors.