SPOKANE -- Witnesses will take the stand Tuesday in the trial of the man accused of a November 2005 crash on Highway 395 that killed five children.

Testimony is underway in the vehicular homicide trial of Clifford Helm, accused of killing five children in a wreck in November 2005. The first prosecution witnesses were drivers who called 911 after seeing Helm cross into oncoming traffic before he slammed into the Schrock family.

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Clifford Helm is on trial for vehicular homicide.

Prosecutors say Helm was on his cell phone and swerving along Highway 395 in North Spokane County on November 1, 2005. For the first time, Helm's attorneys gave their own explanation of what happened: Helm suffered a coughing fit which caused him to lose consciousness. Attorney Carl Oreskovich says the fact Helm never hit the brakes before the crash proves he was not aware of what was happening. Oreskovich says Helm's truck was on cruise control.

Helm's truck crossed the grass median and struck a pickup truck head-on, driven by Jeffrey Schrock and carrying his five children. All five children were killed.

In a final ruling before testimony begins, Judge Michael Price ruled the defense could not use a letter of forgiveness sent to Helm from the Schrock family as evidence. The judge ruled it was not relevant to the case.